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What if you could write more intuitive code that's both flexible and type-safe? The ",[306,504,505],{},"toMap"," function below gives you exactly that - supporting both property names and custom functions:",[299,508,510],{"className":301,"code":509,"filename":303,"language":304,"meta":21,"style":21},"\u002F\u002F Create a map using the 'key' property\nconst map1 = toMap(data, 'key');\n\u002F\u002F ^ const map1: Map\u003Cnumber, Person>\n\n\u002F\u002F Create a map using the 'key' function\nconst map2 = toMap(data, x => x.key);\n\u002F\u002F ^ const map2: Map\u003Cnumber, Person>\n\n\u002F\u002F Create a map using the 'key' property and 'value' property\nconst map3 = toMap(data, 'key', 'name');\n\u002F\u002F ^ const map3: Map\u003Cnumber, string>\n\n\u002F\u002F Create a map using the 'key' function and 'value' function\nconst map4 = toMap(data, x => x.key, x => x.name);\n\u002F\u002F ^ const map4: Map\u003Cnumber, string>\n\n\u002F\u002F Create a map using custom functions\nconst map5 = toMap(data, x => x.birthday, x => `Name: ${x.name}`);\n\u002F\u002F ^ const map5: Map\u003CDate, string>\n\n\u002F\u002F Create a map using no parameters\nconst map6 = toMap(data);\n\u002F\u002F ^ const map6: Map\u003CPerson, Person>\n\n",[306,511,512,517,538,543,547,552,572,577,581,586,608,614,619,625,653,659,664,670,710,716,720,726,741],{"__ignoreMap":21},[309,513,514],{"class":311,"line":20},[309,515,516],{"class":459},"\u002F\u002F Create a map using the 'key' property\n",[309,518,519,521,524,526,529,532,535],{"class":311,"line":131},[309,520,363],{"class":314},[309,522,523],{"class":333}," map1",[309,525,471],{"class":314},[309,527,528],{"class":318}," toMap",[309,530,531],{"class":322},"(data, ",[309,533,534],{"class":393},"'key'",[309,536,537],{"class":322},");\n",[309,539,540],{"class":311,"line":155},[309,541,542],{"class":459},"\u002F\u002F ^ const map1: Map\u003Cnumber, Person>\n",[309,544,545],{"class":311,"line":180},[309,546,448],{"emptyLinePlaceholder":245},[309,548,549],{"class":311,"line":204},[309,550,551],{"class":459},"\u002F\u002F Create a map using the 'key' function\n",[309,553,554,556,559,561,563,565,567,569],{"class":311,"line":445},[309,555,363],{"class":314},[309,557,558],{"class":333}," map2",[309,560,471],{"class":314},[309,562,528],{"class":318},[309,564,531],{"class":322},[309,566,488],{"class":326},[309,568,491],{"class":314},[309,570,571],{"class":322}," x.key);\n",[309,573,574],{"class":311,"line":451},[309,575,576],{"class":459},"\u002F\u002F ^ const map2: Map\u003Cnumber, Person>\n",[309,578,579],{"class":311,"line":456},[309,580,448],{"emptyLinePlaceholder":245},[309,582,583],{"class":311,"line":463},[309,584,585],{"class":459},"\u002F\u002F Create a map using the 'key' property and 'value' property\n",[309,587,588,590,593,595,597,599,601,603,606],{"class":311,"line":41},[309,589,363],{"class":314},[309,591,592],{"class":333}," map3",[309,594,471],{"class":314},[309,596,528],{"class":318},[309,598,531],{"class":322},[309,600,534],{"class":393},[309,602,337],{"class":322},[309,604,605],{"class":393},"'name'",[309,607,537],{"class":322},[309,609,611],{"class":311,"line":610},11,[309,612,613],{"class":459},"\u002F\u002F ^ const map3: Map\u003Cnumber, string>\n",[309,615,617],{"class":311,"line":616},12,[309,618,448],{"emptyLinePlaceholder":245},[309,620,622],{"class":311,"line":621},13,[309,623,624],{"class":459},"\u002F\u002F Create a map using the 'key' function and 'value' function\n",[309,626,628,630,633,635,637,639,641,643,646,648,650],{"class":311,"line":627},14,[309,629,363],{"class":314},[309,631,632],{"class":333}," map4",[309,634,471],{"class":314},[309,636,528],{"class":318},[309,638,531],{"class":322},[309,640,488],{"class":326},[309,642,491],{"class":314},[309,644,645],{"class":322}," x.key, ",[309,647,488],{"class":326},[309,649,491],{"class":314},[309,651,652],{"class":322}," x.name);\n",[309,654,656],{"class":311,"line":655},15,[309,657,658],{"class":459},"\u002F\u002F ^ const map4: Map\u003Cnumber, string>\n",[309,660,662],{"class":311,"line":661},16,[309,663,448],{"emptyLinePlaceholder":245},[309,665,667],{"class":311,"line":666},17,[309,668,669],{"class":459},"\u002F\u002F Create a map using custom functions\n",[309,671,673,675,678,680,682,684,686,688,691,693,695,698,700,703,705,708],{"class":311,"line":672},18,[309,674,363],{"class":314},[309,676,677],{"class":333}," map5",[309,679,471],{"class":314},[309,681,528],{"class":318},[309,683,531],{"class":322},[309,685,488],{"class":326},[309,687,491],{"class":314},[309,689,690],{"class":322}," x.birthday, ",[309,692,488],{"class":326},[309,694,491],{"class":314},[309,696,697],{"class":393}," `Name: ${",[309,699,488],{"class":322},[309,701,702],{"class":393},".",[309,704,340],{"class":322},[309,706,707],{"class":393},"}`",[309,709,537],{"class":322},[309,711,713],{"class":311,"line":712},19,[309,714,715],{"class":459},"\u002F\u002F ^ const map5: Map\u003CDate, string>\n",[309,717,718],{"class":311,"line":55},[309,719,448],{"emptyLinePlaceholder":245},[309,721,723],{"class":311,"line":722},21,[309,724,725],{"class":459},"\u002F\u002F Create a map using no parameters\n",[309,727,729,731,734,736,738],{"class":311,"line":728},22,[309,730,363],{"class":314},[309,732,733],{"class":333}," map6",[309,735,471],{"class":314},[309,737,528],{"class":318},[309,739,740],{"class":322},"(data);\n",[309,742,744],{"class":311,"line":743},23,[309,745,746],{"class":459},"\u002F\u002F ^ const map6: Map\u003CPerson, Person>\n",[231,748,749],{},"Ready to build this powerful utility? Follow along as we construct it step by step. Each iteration will teach you new TypeScript concepts that you can apply to your own projects:\n(click on the edges of the code block to step forward or backward through the versions)",[751,752,754,949,1216,1667,2077,2494,3163],"code-group",{":tabs-as-steps":753},"true",[299,755,757],{"className":301,"code":756,"filename":387,"language":304,"meta":21,"style":21},"\u002F\u002F Start simple - you'll build complexity gradually\nexport function toMap\u003CT, K>(\n array: readonly T[],\n keyFn: ((item: T) => K),\n) {\n if (!array?.length) return new Map\u003CK, T>();\n\n return new Map\u003CK, T>(array.map(item => [keyFn(item), item]));\n}\n\nconst dict = toMap(data, x => x.birthday);\n\u002F\u002F ^ const dict: Map\u003CDate, Person>\n",[306,758,759,764,788,804,833,838,875,879,916,921,925,944],{"__ignoreMap":21},[309,760,761],{"class":311,"line":20},[309,762,763],{"class":459},"\u002F\u002F Start simple - you'll build complexity gradually\n",[309,765,766,769,772,774,777,780,782,785],{"class":311,"line":131},[309,767,768],{"class":314},"export",[309,770,771],{"class":314}," function",[309,773,528],{"class":318},[309,775,776],{"class":322},"\u003C",[309,778,779],{"class":318},"T",[309,781,337],{"class":322},[309,783,784],{"class":318},"K",[309,786,787],{"class":322},">(\n",[309,789,790,793,795,798,801],{"class":311,"line":155},[309,791,792],{"class":326}," array",[309,794,330],{"class":314},[309,796,797],{"class":314}," readonly",[309,799,800],{"class":318}," T",[309,802,803],{"class":322},"[],\n",[309,805,806,809,811,814,817,819,821,824,827,830],{"class":311,"line":180},[309,807,808],{"class":326}," keyFn",[309,810,330],{"class":314},[309,812,813],{"class":322}," ((",[309,815,816],{"class":326},"item",[309,818,330],{"class":314},[309,820,800],{"class":318},[309,822,823],{"class":322},") ",[309,825,826],{"class":314},"=>",[309,828,829],{"class":318}," K",[309,831,832],{"class":322},"),\n",[309,834,835],{"class":311,"line":204},[309,836,837],{"class":322},") {\n",[309,839,840,843,846,849,852,855,857,860,862,864,866,868,870,872],{"class":311,"line":445},[309,841,842],{"class":314}," if",[309,844,845],{"class":322}," (",[309,847,848],{"class":314},"!",[309,850,851],{"class":322},"array?.",[309,853,854],{"class":333},"length",[309,856,823],{"class":322},[309,858,859],{"class":314},"return",[309,861,474],{"class":314},[309,863,477],{"class":318},[309,865,776],{"class":322},[309,867,784],{"class":318},[309,869,337],{"class":322},[309,871,779],{"class":318},[309,873,874],{"class":322},">();\n",[309,876,877],{"class":311,"line":451},[309,878,448],{"emptyLinePlaceholder":245},[309,880,881,884,886,888,890,892,894,896,899,901,903,905,907,910,913],{"class":311,"line":456},[309,882,883],{"class":314}," return",[309,885,474],{"class":314},[309,887,477],{"class":318},[309,889,776],{"class":322},[309,891,784],{"class":318},[309,893,337],{"class":322},[309,895,779],{"class":318},[309,897,898],{"class":322},">(array.",[309,900,483],{"class":318},[309,902,405],{"class":322},[309,904,816],{"class":326},[309,906,491],{"class":314},[309,908,909],{"class":322}," [",[309,911,912],{"class":318},"keyFn",[309,914,915],{"class":322},"(item), item]));\n",[309,917,918],{"class":311,"line":463},[309,919,920],{"class":322},"}\n",[309,922,923],{"class":311,"line":41},[309,924,448],{"emptyLinePlaceholder":245},[309,926,927,929,931,933,935,937,939,941],{"class":311,"line":610},[309,928,363],{"class":314},[309,930,468],{"class":333},[309,932,471],{"class":314},[309,934,528],{"class":318},[309,936,531],{"class":322},[309,938,488],{"class":326},[309,940,491],{"class":314},[309,942,943],{"class":322}," x.birthday);\n",[309,945,946],{"class":311,"line":616},[309,947,948],{"class":459},"\u002F\u002F ^ const dict: Map\u003CDate, Person>\n",[299,950,952],{"className":301,"code":951,"filename":418,"language":304,"meta":21,"style":21},"\u002F\u002F We add some spacing to go through the steps without lines jumping around\n\nexport function toMap\u003C\n T, \n K\n\n>(\n array: readonly T[],\n keyFn: ((item: T) => K),\n\n) {\n\n\n\n\n\n\n\n\n\n if (!array?.length) return new Map\u003CK, T>();\n\n\n\n\n\n\n\n\n\n return new Map\u003CK, T>(array.map(item => [keyFn(item), item]));\n}\n\n\nconst dict = toMap(data, x => x.birthday);\n\u002F\u002F ^ const dict: Map\u003CDate, Person>\n\n",[306,953,954,959,963,974,982,987,991,995,1007,1029,1033,1037,1041,1045,1049,1053,1057,1061,1065,1069,1073,1103,1107,1111,1116,1121,1126,1131,1136,1141,1145,1178,1182,1187,1192,1211],{"__ignoreMap":21},[309,955,956],{"class":311,"line":20},[309,957,958],{"class":459},"\u002F\u002F We add some spacing to go through the steps without lines jumping around\n",[309,960,961],{"class":311,"line":131},[309,962,448],{"emptyLinePlaceholder":245},[309,964,965,967,969,971],{"class":311,"line":155},[309,966,768],{"class":314},[309,968,771],{"class":314},[309,970,528],{"class":318},[309,972,973],{"class":322},"\u003C\n",[309,975,976,979],{"class":311,"line":180},[309,977,978],{"class":318}," T",[309,980,981],{"class":322},", \n",[309,983,984],{"class":311,"line":204},[309,985,986],{"class":318}," K\n",[309,988,989],{"class":311,"line":445},[309,990,448],{"emptyLinePlaceholder":245},[309,992,993],{"class":311,"line":451},[309,994,787],{"class":322},[309,996,997,999,1001,1003,1005],{"class":311,"line":456},[309,998,792],{"class":326},[309,1000,330],{"class":314},[309,1002,797],{"class":314},[309,1004,800],{"class":318},[309,1006,803],{"class":322},[309,1008,1009,1011,1013,1015,1017,1019,1021,1023,1025,1027],{"class":311,"line":463},[309,1010,808],{"class":326},[309,1012,330],{"class":314},[309,1014,813],{"class":322},[309,1016,816],{"class":326},[309,1018,330],{"class":314},[309,1020,800],{"class":318},[309,1022,823],{"class":322},[309,1024,826],{"class":314},[309,1026,829],{"class":318},[309,1028,832],{"class":322},[309,1030,1031],{"class":311,"line":41},[309,1032,448],{"emptyLinePlaceholder":245},[309,1034,1035],{"class":311,"line":610},[309,1036,837],{"class":322},[309,1038,1039],{"class":311,"line":616},[309,1040,448],{"emptyLinePlaceholder":245},[309,1042,1043],{"class":311,"line":621},[309,1044,448],{"emptyLinePlaceholder":245},[309,1046,1047],{"class":311,"line":627},[309,1048,448],{"emptyLinePlaceholder":245},[309,1050,1051],{"class":311,"line":655},[309,1052,448],{"emptyLinePlaceholder":245},[309,1054,1055],{"class":311,"line":661},[309,1056,448],{"emptyLinePlaceholder":245},[309,1058,1059],{"class":311,"line":666},[309,1060,448],{"emptyLinePlaceholder":245},[309,1062,1063],{"class":311,"line":672},[309,1064,448],{"emptyLinePlaceholder":245},[309,1066,1067],{"class":311,"line":712},[309,1068,448],{"emptyLinePlaceholder":245},[309,1070,1071],{"class":311,"line":55},[309,1072,448],{"emptyLinePlaceholder":245},[309,1074,1075,1077,1079,1081,1083,1085,1087,1089,1091,1093,1095,1097,1099,1101],{"class":311,"line":722},[309,1076,842],{"class":314},[309,1078,845],{"class":322},[309,1080,848],{"class":314},[309,1082,851],{"class":322},[309,1084,854],{"class":333},[309,1086,823],{"class":322},[309,1088,859],{"class":314},[309,1090,474],{"class":314},[309,1092,477],{"class":318},[309,1094,776],{"class":322},[309,1096,784],{"class":318},[309,1098,337],{"class":322},[309,1100,779],{"class":318},[309,1102,874],{"class":322},[309,1104,1105],{"class":311,"line":728},[309,1106,448],{"emptyLinePlaceholder":245},[309,1108,1109],{"class":311,"line":743},[309,1110,448],{"emptyLinePlaceholder":245},[309,1112,1114],{"class":311,"line":1113},24,[309,1115,448],{"emptyLinePlaceholder":245},[309,1117,1119],{"class":311,"line":1118},25,[309,1120,448],{"emptyLinePlaceholder":245},[309,1122,1124],{"class":311,"line":1123},26,[309,1125,448],{"emptyLinePlaceholder":245},[309,1127,1129],{"class":311,"line":1128},27,[309,1130,448],{"emptyLinePlaceholder":245},[309,1132,1134],{"class":311,"line":1133},28,[309,1135,448],{"emptyLinePlaceholder":245},[309,1137,1139],{"class":311,"line":1138},29,[309,1140,448],{"emptyLinePlaceholder":245},[309,1142,1143],{"class":311,"line":69},[309,1144,448],{"emptyLinePlaceholder":245},[309,1146,1148,1150,1152,1154,1156,1158,1160,1162,1164,1166,1168,1170,1172,1174,1176],{"class":311,"line":1147},31,[309,1149,883],{"class":314},[309,1151,474],{"class":314},[309,1153,477],{"class":318},[309,1155,776],{"class":322},[309,1157,784],{"class":318},[309,1159,337],{"class":322},[309,1161,779],{"class":318},[309,1163,898],{"class":322},[309,1165,483],{"class":318},[309,1167,405],{"class":322},[309,1169,816],{"class":326},[309,1171,491],{"class":314},[309,1173,909],{"class":322},[309,1175,912],{"class":318},[309,1177,915],{"class":322},[309,1179,1180],{"class":311,"line":244},[309,1181,920],{"class":322},[309,1183,1185],{"class":311,"line":1184},33,[309,1186,448],{"emptyLinePlaceholder":245},[309,1188,1190],{"class":311,"line":1189},34,[309,1191,448],{"emptyLinePlaceholder":245},[309,1193,1195,1197,1199,1201,1203,1205,1207,1209],{"class":311,"line":1194},35,[309,1196,363],{"class":314},[309,1198,468],{"class":333},[309,1200,471],{"class":314},[309,1202,528],{"class":318},[309,1204,531],{"class":322},[309,1206,488],{"class":326},[309,1208,491],{"class":314},[309,1210,943],{"class":322},[309,1212,1214],{"class":311,"line":1213},36,[309,1215,948],{"class":459},[299,1217,1221],{"className":1218,"code":1219,"filename":1220,"language":304,"meta":21,"style":21},"language-typescript shiki shiki-themes github-light github-dark has-highlighted","\u002F\u002F Now you'll learn conditional types - expand the key parameter to accept property names [!code highlight]\n\u002F\u002F and move the key type to generics so you can reference it later [!code highlight]\nexport function toMap\u003C\n T, \n K, \n KF extends keyof T | ((item: T) => K) \u002F\u002F [!code highlight]\n>(\n array: readonly T[],\n key: KF, \u002F\u002F [!code highlight]\n\n) {\n \u002F\u002F - Create your first conditional type - it chooses between property type or function return type [!code highlight]\n type TKeyType = KF extends keyof T \u002F\u002F [!code highlight]\n ? T[KF] \u002F\u002F [!code highlight]\n : KF extends ((item: T) => K) \u002F\u002F [!code highlight]\n ? K \u002F\u002F [!code highlight]\n : never; \u002F\u002F [!code highlight]\n\n\n\n if (!array?.length) return new Map\u003CTKeyType, T>();\n\n \u002F\u002F - You'll hit a TypeScript error here - Type 'K' is not assignable to type 'TKeyType' [!code highlight]\n const keyFn: (item: T) => TKeyType \u002F\u002F [!code highlight]\n = typeof key === 'function'\n ? key\n : typeof array[0] === 'object' && array[0] !== null\n ? item => item[key as keyof T]\n : item => item; \u002F\u002F Fallback when the array contains primitive values\n\n return new Map\u003CTKeyType, T>(array.map(item => [keyFn(item), item]));\n}\n\n\u002F\u002F - Not the type safety you want yet [!code highlight]\nconst dict = toMap(data, x => x.birthday); \u002F\u002F [!code highlight]\n\u002F\u002F ^ const dict: Map\u003Cunknown, Person> [!code highlight]\n","3",[306,1222,1223,1228,1235,1246,1252,1259,1292,1296,1308,1321,1325,1329,1334,1353,1370,1397,1405,1417,1421,1425,1429,1460,1464,1469,1494,1511,1519,1555,1578,1593,1597,1629,1633,1637,1642,1662],{"__ignoreMap":21},[309,1224,1225],{"class":311,"line":20},[309,1226,1227],{"class":459},"\u002F\u002F Now you'll learn conditional types - expand the key parameter to accept property names",[309,1229,1232],{"class":1230,"line":131},[311,1231],"highlighted",[309,1233,1234],{"class":459},"\u002F\u002F and move the key type to generics so you can reference it later",[309,1236,1238,1240,1242,1244],{"class":1237,"line":155},[311,1231],[309,1239,768],{"class":314},[309,1241,771],{"class":314},[309,1243,528],{"class":318},[309,1245,973],{"class":322},[309,1247,1248,1250],{"class":311,"line":180},[309,1249,978],{"class":318},[309,1251,981],{"class":322},[309,1253,1254,1257],{"class":311,"line":204},[309,1255,1256],{"class":318}," K",[309,1258,981],{"class":322},[309,1260,1262,1265,1268,1271,1273,1276,1278,1280,1282,1284,1286,1288,1290],{"class":1261,"line":445},[311,1231],[309,1263,1264],{"class":318}," KF",[309,1266,1267],{"class":314}," extends",[309,1269,1270],{"class":314}," keyof",[309,1272,800],{"class":318},[309,1274,1275],{"class":314}," |",[309,1277,813],{"class":322},[309,1279,816],{"class":326},[309,1281,330],{"class":314},[309,1283,800],{"class":318},[309,1285,823],{"class":322},[309,1287,826],{"class":314},[309,1289,829],{"class":318},[309,1291,823],{"class":322},[309,1293,1294],{"class":311,"line":451},[309,1295,787],{"class":322},[309,1297,1298,1300,1302,1304,1306],{"class":311,"line":456},[309,1299,792],{"class":326},[309,1301,330],{"class":314},[309,1303,797],{"class":314},[309,1305,800],{"class":318},[309,1307,803],{"class":322},[309,1309,1311,1314,1316,1319],{"class":1310,"line":463},[311,1231],[309,1312,1313],{"class":326}," key",[309,1315,330],{"class":314},[309,1317,1318],{"class":318}," KF",[309,1320,337],{"class":322},[309,1322,1323],{"class":311,"line":41},[309,1324,448],{"emptyLinePlaceholder":245},[309,1326,1327],{"class":311,"line":610},[309,1328,837],{"class":322},[309,1330,1331],{"class":311,"line":616},[309,1332,1333],{"class":459}," \u002F\u002F - Create your first conditional type - it chooses between property type or function return type",[309,1335,1337,1340,1343,1345,1347,1349,1351],{"class":1336,"line":621},[311,1231],[309,1338,1339],{"class":314}," type",[309,1341,1342],{"class":318}," TKeyType",[309,1344,471],{"class":314},[309,1346,1318],{"class":318},[309,1348,1267],{"class":314},[309,1350,1270],{"class":314},[309,1352,800],{"class":318},[309,1354,1356,1359,1361,1364,1367],{"class":1355,"line":627},[311,1231],[309,1357,1358],{"class":314}," ?",[309,1360,800],{"class":318},[309,1362,1363],{"class":322},"[",[309,1365,1366],{"class":318},"KF",[309,1368,1369],{"class":322},"] ",[309,1371,1373,1376,1378,1380,1382,1384,1386,1388,1390,1392,1394],{"class":1372,"line":655},[311,1231],[309,1374,1375],{"class":314}," :",[309,1377,1318],{"class":318},[309,1379,1267],{"class":314},[309,1381,813],{"class":322},[309,1383,816],{"class":326},[309,1385,330],{"class":314},[309,1387,800],{"class":318},[309,1389,823],{"class":322},[309,1391,826],{"class":314},[309,1393,829],{"class":318},[309,1395,1396],{"class":322},") ",[309,1398,1400,1403],{"class":1399,"line":661},[311,1231],[309,1401,1402],{"class":314}," ?",[309,1404,829],{"class":318},[309,1406,1408,1411,1414],{"class":1407,"line":666},[311,1231],[309,1409,1410],{"class":314}," :",[309,1412,1413],{"class":333}," never",[309,1415,1416],{"class":322},"; ",[309,1418,1419],{"class":311,"line":672},[309,1420,448],{"emptyLinePlaceholder":245},[309,1422,1423],{"class":311,"line":712},[309,1424,448],{"emptyLinePlaceholder":245},[309,1426,1427],{"class":311,"line":55},[309,1428,448],{"emptyLinePlaceholder":245},[309,1430,1431,1433,1435,1437,1439,1441,1443,1445,1447,1449,1451,1454,1456,1458],{"class":311,"line":722},[309,1432,842],{"class":314},[309,1434,845],{"class":322},[309,1436,848],{"class":314},[309,1438,851],{"class":322},[309,1440,854],{"class":333},[309,1442,823],{"class":322},[309,1444,859],{"class":314},[309,1446,474],{"class":314},[309,1448,477],{"class":318},[309,1450,776],{"class":322},[309,1452,1453],{"class":318},"TKeyType",[309,1455,337],{"class":322},[309,1457,779],{"class":318},[309,1459,874],{"class":322},[309,1461,1462],{"class":311,"line":728},[309,1463,448],{"emptyLinePlaceholder":245},[309,1465,1466],{"class":311,"line":743},[309,1467,1468],{"class":459}," \u002F\u002F - You'll hit a TypeScript error here - Type 'K' is not assignable to type 'TKeyType'",[309,1470,1472,1475,1478,1480,1482,1484,1486,1488,1490,1492],{"class":1471,"line":1113},[311,1231],[309,1473,1474],{"class":314}," const",[309,1476,1477],{"class":318}," keyFn",[309,1479,330],{"class":314},[309,1481,845],{"class":322},[309,1483,816],{"class":326},[309,1485,330],{"class":314},[309,1487,800],{"class":318},[309,1489,823],{"class":322},[309,1491,826],{"class":314},[309,1493,1342],{"class":318},[309,1495,1496,1499,1502,1505,1508],{"class":311,"line":1118},[309,1497,1498],{"class":314}," =",[309,1500,1501],{"class":314}," typeof",[309,1503,1504],{"class":322}," key ",[309,1506,1507],{"class":314},"===",[309,1509,1510],{"class":393}," 'function'\n",[309,1512,1513,1516],{"class":311,"line":1123},[309,1514,1515],{"class":314}," ?",[309,1517,1518],{"class":322}," key\n",[309,1520,1521,1524,1526,1529,1532,1535,1537,1540,1543,1545,1547,1549,1552],{"class":311,"line":1128},[309,1522,1523],{"class":314}," :",[309,1525,1501],{"class":314},[309,1527,1528],{"class":322}," array[",[309,1530,1531],{"class":333},"0",[309,1533,1534],{"class":322},"] ",[309,1536,1507],{"class":314},[309,1538,1539],{"class":393}," 'object'",[309,1541,1542],{"class":314}," &&",[309,1544,1528],{"class":322},[309,1546,1531],{"class":333},[309,1548,1534],{"class":322},[309,1550,1551],{"class":314},"!==",[309,1553,1554],{"class":333}," null\n",[309,1556,1557,1560,1563,1565,1568,1571,1573,1575],{"class":311,"line":1133},[309,1558,1559],{"class":314}," ?",[309,1561,1562],{"class":326}," item",[309,1564,491],{"class":314},[309,1566,1567],{"class":322}," item[key ",[309,1569,1570],{"class":314},"as",[309,1572,1270],{"class":314},[309,1574,800],{"class":318},[309,1576,1577],{"class":322},"]\n",[309,1579,1580,1583,1585,1587,1590],{"class":311,"line":1138},[309,1581,1582],{"class":314}," :",[309,1584,1562],{"class":326},[309,1586,491],{"class":314},[309,1588,1589],{"class":322}," item; ",[309,1591,1592],{"class":459},"\u002F\u002F Fallback when the array contains primitive values\n",[309,1594,1595],{"class":311,"line":69},[309,1596,448],{"emptyLinePlaceholder":245},[309,1598,1599,1601,1603,1605,1607,1609,1611,1613,1615,1617,1619,1621,1623,1625,1627],{"class":311,"line":1147},[309,1600,883],{"class":314},[309,1602,474],{"class":314},[309,1604,477],{"class":318},[309,1606,776],{"class":322},[309,1608,1453],{"class":318},[309,1610,337],{"class":322},[309,1612,779],{"class":318},[309,1614,898],{"class":322},[309,1616,483],{"class":318},[309,1618,405],{"class":322},[309,1620,816],{"class":326},[309,1622,491],{"class":314},[309,1624,909],{"class":322},[309,1626,912],{"class":318},[309,1628,915],{"class":322},[309,1630,1631],{"class":311,"line":244},[309,1632,920],{"class":322},[309,1634,1635],{"class":311,"line":1184},[309,1636,448],{"emptyLinePlaceholder":245},[309,1638,1639],{"class":311,"line":1189},[309,1640,1641],{"class":459},"\u002F\u002F - Not the type safety you want yet",[309,1643,1645,1647,1649,1651,1653,1655,1657,1659],{"class":1644,"line":1194},[311,1231],[309,1646,363],{"class":314},[309,1648,468],{"class":333},[309,1650,471],{"class":314},[309,1652,528],{"class":318},[309,1654,531],{"class":322},[309,1656,488],{"class":326},[309,1658,491],{"class":314},[309,1660,1661],{"class":322}," x.birthday); ",[309,1663,1664],{"class":311,"line":1213},[309,1665,1666],{"class":459},"\u002F\u002F ^ const dict: Map\u003Cunknown, Person>",[299,1668,1671],{"className":1218,"code":1669,"filename":1670,"language":304,"meta":21,"style":21},"\u002F\u002F Here's how you solve the error - use type inference instead [!code highlight]\n\u002F\u002F - Remove the K type parameter and let TypeScript infer it [!code highlight]\nexport function toMap\u003C\n T,\n \n KF extends keyof T | ((item: T) => any) \u002F\u002F [!code highlight]\n>(\n array: readonly T[],\n key: KF, \u002F\u002F [!code highlight]\n\n) {\n \u002F\u002F - Let TypeScript infer the return type for you [!code highlight]\n type TKeyType = KF extends keyof T \n ? T[KF] \n : KF extends ((item: T) => infer K) \u002F\u002F [!code highlight]\n ? K \n : never; \n\n\n\n if (!array?.length) return new Map\u003CTKeyType, T>();\n\n \n const keyFn: (item: T) => TKeyType\n = typeof key === 'function'\n ? key\n : typeof array[0] === 'object' && array[0] !== null\n ? item => item[key as keyof T]\n : item => item; \n\n return new Map\u003CTKeyType, T>(array.map(item => [keyFn(item), item]));\n}\n\n\u002F\u002F - Perfect! Now you get proper type inference [!code highlight]\nconst dict = toMap(data, x => x.birthday); \u002F\u002F [!code highlight]\n\u002F\u002F ^ const dict: Map\u003CDate, Person> [!code highlight]\n","4",[306,1672,1673,1678,1684,1695,1702,1707,1737,1741,1753,1764,1768,1772,1777,1797,1810,1838,1847,1856,1860,1864,1868,1898,1902,1906,1929,1941,1947,1975,1993,2004,2008,2040,2044,2048,2053,2072],{"__ignoreMap":21},[309,1674,1675],{"class":311,"line":20},[309,1676,1677],{"class":459},"\u002F\u002F Here's how you solve the error - use type inference instead",[309,1679,1681],{"class":1680,"line":131},[311,1231],[309,1682,1683],{"class":459},"\u002F\u002F - Remove the K type parameter and let TypeScript infer it",[309,1685,1687,1689,1691,1693],{"class":1686,"line":155},[311,1231],[309,1688,768],{"class":314},[309,1690,771],{"class":314},[309,1692,528],{"class":318},[309,1694,973],{"class":322},[309,1696,1697,1699],{"class":311,"line":180},[309,1698,978],{"class":318},[309,1700,1701],{"class":322},",\n",[309,1703,1704],{"class":311,"line":204},[309,1705,1706],{"class":322}," \n",[309,1708,1710,1712,1714,1716,1718,1720,1722,1724,1726,1728,1730,1732,1735],{"class":1709,"line":445},[311,1231],[309,1711,1264],{"class":318},[309,1713,1267],{"class":314},[309,1715,1270],{"class":314},[309,1717,800],{"class":318},[309,1719,1275],{"class":314},[309,1721,813],{"class":322},[309,1723,816],{"class":326},[309,1725,330],{"class":314},[309,1727,800],{"class":318},[309,1729,823],{"class":322},[309,1731,826],{"class":314},[309,1733,1734],{"class":333}," any",[309,1736,823],{"class":322},[309,1738,1739],{"class":311,"line":451},[309,1740,787],{"class":322},[309,1742,1743,1745,1747,1749,1751],{"class":311,"line":456},[309,1744,792],{"class":326},[309,1746,330],{"class":314},[309,1748,797],{"class":314},[309,1750,800],{"class":318},[309,1752,803],{"class":322},[309,1754,1756,1758,1760,1762],{"class":1755,"line":463},[311,1231],[309,1757,1313],{"class":326},[309,1759,330],{"class":314},[309,1761,1318],{"class":318},[309,1763,337],{"class":322},[309,1765,1766],{"class":311,"line":41},[309,1767,448],{"emptyLinePlaceholder":245},[309,1769,1770],{"class":311,"line":610},[309,1771,837],{"class":322},[309,1773,1774],{"class":311,"line":616},[309,1775,1776],{"class":459}," \u002F\u002F - Let TypeScript infer the return type for you",[309,1778,1780,1782,1784,1786,1788,1790,1792,1794],{"class":1779,"line":621},[311,1231],[309,1781,1339],{"class":314},[309,1783,1342],{"class":318},[309,1785,471],{"class":314},[309,1787,1318],{"class":318},[309,1789,1267],{"class":314},[309,1791,1270],{"class":314},[309,1793,800],{"class":318},[309,1795,1796],{"class":322}," \n",[309,1798,1799,1801,1803,1805,1807],{"class":311,"line":627},[309,1800,1358],{"class":314},[309,1802,800],{"class":318},[309,1804,1363],{"class":322},[309,1806,1366],{"class":318},[309,1808,1809],{"class":322},"] \n",[309,1811,1813,1815,1817,1819,1821,1823,1825,1827,1829,1831,1834,1836],{"class":1812,"line":655},[311,1231],[309,1814,1375],{"class":314},[309,1816,1318],{"class":318},[309,1818,1267],{"class":314},[309,1820,813],{"class":322},[309,1822,816],{"class":326},[309,1824,330],{"class":314},[309,1826,800],{"class":318},[309,1828,823],{"class":322},[309,1830,826],{"class":314},[309,1832,1833],{"class":314}," infer",[309,1835,829],{"class":318},[309,1837,823],{"class":322},[309,1839,1840,1842,1844],{"class":311,"line":661},[309,1841,1402],{"class":314},[309,1843,829],{"class":318},[309,1845,1846],{"class":322}," \n",[309,1848,1849,1851,1853],{"class":311,"line":666},[309,1850,1410],{"class":314},[309,1852,1413],{"class":333},[309,1854,1855],{"class":322},"; \n",[309,1857,1858],{"class":311,"line":672},[309,1859,448],{"emptyLinePlaceholder":245},[309,1861,1862],{"class":311,"line":712},[309,1863,448],{"emptyLinePlaceholder":245},[309,1865,1866],{"class":311,"line":55},[309,1867,448],{"emptyLinePlaceholder":245},[309,1869,1870,1872,1874,1876,1878,1880,1882,1884,1886,1888,1890,1892,1894,1896],{"class":311,"line":722},[309,1871,842],{"class":314},[309,1873,845],{"class":322},[309,1875,848],{"class":314},[309,1877,851],{"class":322},[309,1879,854],{"class":333},[309,1881,823],{"class":322},[309,1883,859],{"class":314},[309,1885,474],{"class":314},[309,1887,477],{"class":318},[309,1889,776],{"class":322},[309,1891,1453],{"class":318},[309,1893,337],{"class":322},[309,1895,779],{"class":318},[309,1897,874],{"class":322},[309,1899,1900],{"class":311,"line":728},[309,1901,448],{"emptyLinePlaceholder":245},[309,1903,1904],{"class":311,"line":743},[309,1905,1796],{"class":322},[309,1907,1908,1910,1912,1914,1916,1918,1920,1922,1924,1926],{"class":311,"line":1113},[309,1909,1474],{"class":314},[309,1911,1477],{"class":318},[309,1913,330],{"class":314},[309,1915,845],{"class":322},[309,1917,816],{"class":326},[309,1919,330],{"class":314},[309,1921,800],{"class":318},[309,1923,823],{"class":322},[309,1925,826],{"class":314},[309,1927,1928],{"class":318}," TKeyType\n",[309,1930,1931,1933,1935,1937,1939],{"class":311,"line":1118},[309,1932,1498],{"class":314},[309,1934,1501],{"class":314},[309,1936,1504],{"class":322},[309,1938,1507],{"class":314},[309,1940,1510],{"class":393},[309,1942,1943,1945],{"class":311,"line":1123},[309,1944,1515],{"class":314},[309,1946,1518],{"class":322},[309,1948,1949,1951,1953,1955,1957,1959,1961,1963,1965,1967,1969,1971,1973],{"class":311,"line":1128},[309,1950,1523],{"class":314},[309,1952,1501],{"class":314},[309,1954,1528],{"class":322},[309,1956,1531],{"class":333},[309,1958,1534],{"class":322},[309,1960,1507],{"class":314},[309,1962,1539],{"class":393},[309,1964,1542],{"class":314},[309,1966,1528],{"class":322},[309,1968,1531],{"class":333},[309,1970,1534],{"class":322},[309,1972,1551],{"class":314},[309,1974,1554],{"class":333},[309,1976,1977,1979,1981,1983,1985,1987,1989,1991],{"class":311,"line":1133},[309,1978,1559],{"class":314},[309,1980,1562],{"class":326},[309,1982,491],{"class":314},[309,1984,1567],{"class":322},[309,1986,1570],{"class":314},[309,1988,1270],{"class":314},[309,1990,800],{"class":318},[309,1992,1577],{"class":322},[309,1994,1995,1997,1999,2001],{"class":311,"line":1138},[309,1996,1582],{"class":314},[309,1998,1562],{"class":326},[309,2000,491],{"class":314},[309,2002,2003],{"class":322}," item; \n",[309,2005,2006],{"class":311,"line":69},[309,2007,448],{"emptyLinePlaceholder":245},[309,2009,2010,2012,2014,2016,2018,2020,2022,2024,2026,2028,2030,2032,2034,2036,2038],{"class":311,"line":1147},[309,2011,883],{"class":314},[309,2013,474],{"class":314},[309,2015,477],{"class":318},[309,2017,776],{"class":322},[309,2019,1453],{"class":318},[309,2021,337],{"class":322},[309,2023,779],{"class":318},[309,2025,898],{"class":322},[309,2027,483],{"class":318},[309,2029,405],{"class":322},[309,2031,816],{"class":326},[309,2033,491],{"class":314},[309,2035,909],{"class":322},[309,2037,912],{"class":318},[309,2039,915],{"class":322},[309,2041,2042],{"class":311,"line":244},[309,2043,920],{"class":322},[309,2045,2046],{"class":311,"line":1184},[309,2047,448],{"emptyLinePlaceholder":245},[309,2049,2050],{"class":311,"line":1189},[309,2051,2052],{"class":459},"\u002F\u002F - Perfect! Now you get proper type inference",[309,2054,2056,2058,2060,2062,2064,2066,2068,2070],{"class":2055,"line":1194},[311,1231],[309,2057,363],{"class":314},[309,2059,468],{"class":333},[309,2061,471],{"class":314},[309,2063,528],{"class":318},[309,2065,531],{"class":322},[309,2067,488],{"class":326},[309,2069,491],{"class":314},[309,2071,1661],{"class":322},[309,2073,2074],{"class":311,"line":1213},[309,2075,2076],{"class":459},"\u002F\u002F ^ const dict: Map\u003CDate, Person>",[299,2078,2081],{"className":1218,"code":2079,"filename":2080,"language":304,"meta":21,"style":21},"\u002F\u002F Make the function more flexible - optional parameters allow you to do more [!code highlight]\n\nexport function toMap\u003C\n T,\n\n KF extends keyof T | ((item: T) => any) | undefined, \u002F\u002F [!code highlight]\n>(\n array: readonly T[],\n key?: KF, \u002F\u002F [!code highlight]\n\n) {\n \u002F\u002F - Handle the optional case in your conditional types, by returning T [!code highlight]\n type TKeyType = undefined extends KF \u002F\u002F [!code highlight]\n ? T \u002F\u002F [!code highlight]\n : KF extends keyof T\n ? T[KF]\n : KF extends ((item: T) => infer K)\n ? K\n : never;\n\n if (!array?.length)\n return new Map\u003CTKeyType, T>();\n\n const keyFn: (item: T) => TKeyType\n = typeof key === 'function'\n ? key\n : key !== undefined && typeof array[0] === 'object' && array[0] !== null \u002F\u002F [!code highlight]\n ? item => item[key as keyof T]\n : item => item;\n\n return new Map\u003CTKeyType, T>(array.map(item => [keyFn(item), item]));\n}\n\n\nconst dict = toMap(data);\n\u002F\u002F ^ const dict: Map\u003CPerson, Person> [!code highlight]\n","5",[306,2082,2083,2088,2093,2103,2109,2113,2150,2154,2166,2178,2182,2186,2191,2206,2213,2226,2238,2265,2272,2281,2285,2299,2318,2322,2344,2356,2362,2400,2418,2429,2433,2465,2469,2473,2477,2489],{"__ignoreMap":21},[309,2084,2085],{"class":311,"line":20},[309,2086,2087],{"class":459},"\u002F\u002F Make the function more flexible - optional parameters allow you to do more",[309,2089,2091],{"class":2090,"line":131},[311,1231],[309,2092,448],{"emptyLinePlaceholder":245},[309,2094,2095,2097,2099,2101],{"class":311,"line":155},[309,2096,768],{"class":314},[309,2098,771],{"class":314},[309,2100,528],{"class":318},[309,2102,973],{"class":322},[309,2104,2105,2107],{"class":311,"line":180},[309,2106,978],{"class":318},[309,2108,1701],{"class":322},[309,2110,2111],{"class":311,"line":204},[309,2112,448],{"emptyLinePlaceholder":245},[309,2114,2116,2118,2120,2122,2124,2126,2128,2130,2132,2134,2136,2138,2140,2142,2145,2148],{"class":2115,"line":445},[311,1231],[309,2117,1264],{"class":318},[309,2119,1267],{"class":314},[309,2121,1270],{"class":314},[309,2123,800],{"class":318},[309,2125,1275],{"class":314},[309,2127,813],{"class":322},[309,2129,816],{"class":326},[309,2131,330],{"class":314},[309,2133,800],{"class":318},[309,2135,823],{"class":322},[309,2137,826],{"class":314},[309,2139,1734],{"class":333},[309,2141,823],{"class":322},[309,2143,2144],{"class":314},"|",[309,2146,2147],{"class":333}," undefined",[309,2149,337],{"class":322},[309,2151,2152],{"class":311,"line":451},[309,2153,787],{"class":322},[309,2155,2156,2158,2160,2162,2164],{"class":311,"line":456},[309,2157,792],{"class":326},[309,2159,330],{"class":314},[309,2161,797],{"class":314},[309,2163,800],{"class":318},[309,2165,803],{"class":322},[309,2167,2169,2171,2174,2176],{"class":2168,"line":463},[311,1231],[309,2170,1313],{"class":326},[309,2172,2173],{"class":314},"?:",[309,2175,1318],{"class":318},[309,2177,337],{"class":322},[309,2179,2180],{"class":311,"line":41},[309,2181,448],{"emptyLinePlaceholder":245},[309,2183,2184],{"class":311,"line":610},[309,2185,837],{"class":322},[309,2187,2188],{"class":311,"line":616},[309,2189,2190],{"class":459}," \u002F\u002F - Handle the optional case in your conditional types, by returning T",[309,2192,2194,2196,2198,2200,2202,2204],{"class":2193,"line":621},[311,1231],[309,2195,1339],{"class":314},[309,2197,1342],{"class":318},[309,2199,471],{"class":314},[309,2201,2147],{"class":333},[309,2203,1267],{"class":314},[309,2205,1318],{"class":318},[309,2207,2209,2211],{"class":2208,"line":627},[311,1231],[309,2210,1402],{"class":314},[309,2212,800],{"class":318},[309,2214,2215,2217,2219,2221,2223],{"class":311,"line":655},[309,2216,1410],{"class":314},[309,2218,1318],{"class":318},[309,2220,1267],{"class":314},[309,2222,1270],{"class":314},[309,2224,2225],{"class":318}," T\n",[309,2227,2228,2230,2232,2234,2236],{"class":311,"line":661},[309,2229,1515],{"class":314},[309,2231,800],{"class":318},[309,2233,1363],{"class":322},[309,2235,1366],{"class":318},[309,2237,1577],{"class":322},[309,2239,2240,2242,2244,2246,2248,2250,2252,2254,2256,2258,2260,2262],{"class":311,"line":666},[309,2241,1523],{"class":314},[309,2243,1318],{"class":318},[309,2245,1267],{"class":314},[309,2247,813],{"class":322},[309,2249,816],{"class":326},[309,2251,330],{"class":314},[309,2253,800],{"class":318},[309,2255,823],{"class":322},[309,2257,826],{"class":314},[309,2259,1833],{"class":314},[309,2261,829],{"class":318},[309,2263,2264],{"class":322},")\n",[309,2266,2267,2269],{"class":311,"line":672},[309,2268,1559],{"class":314},[309,2270,2271],{"class":318}," K\n",[309,2273,2274,2276,2278],{"class":311,"line":712},[309,2275,1582],{"class":314},[309,2277,1413],{"class":333},[309,2279,2280],{"class":322},";\n",[309,2282,2283],{"class":311,"line":55},[309,2284,448],{"emptyLinePlaceholder":245},[309,2286,2287,2289,2291,2293,2295,2297],{"class":311,"line":722},[309,2288,842],{"class":314},[309,2290,845],{"class":322},[309,2292,848],{"class":314},[309,2294,851],{"class":322},[309,2296,854],{"class":333},[309,2298,2264],{"class":322},[309,2300,2301,2304,2306,2308,2310,2312,2314,2316],{"class":311,"line":728},[309,2302,2303],{"class":314}," return",[309,2305,474],{"class":314},[309,2307,477],{"class":318},[309,2309,776],{"class":322},[309,2311,1453],{"class":318},[309,2313,337],{"class":322},[309,2315,779],{"class":318},[309,2317,874],{"class":322},[309,2319,2320],{"class":311,"line":743},[309,2321,448],{"emptyLinePlaceholder":245},[309,2323,2324,2326,2328,2330,2332,2334,2336,2338,2340,2342],{"class":311,"line":1113},[309,2325,1474],{"class":314},[309,2327,1477],{"class":318},[309,2329,330],{"class":314},[309,2331,845],{"class":322},[309,2333,816],{"class":326},[309,2335,330],{"class":314},[309,2337,800],{"class":318},[309,2339,823],{"class":322},[309,2341,826],{"class":314},[309,2343,1928],{"class":318},[309,2345,2346,2348,2350,2352,2354],{"class":311,"line":1118},[309,2347,1498],{"class":314},[309,2349,1501],{"class":314},[309,2351,1504],{"class":322},[309,2353,1507],{"class":314},[309,2355,1510],{"class":393},[309,2357,2358,2360],{"class":311,"line":1123},[309,2359,1515],{"class":314},[309,2361,1518],{"class":322},[309,2363,2365,2367,2369,2371,2373,2375,2377,2379,2381,2383,2385,2387,2389,2391,2393,2395,2397],{"class":2364,"line":1128},[311,1231],[309,2366,1523],{"class":314},[309,2368,1504],{"class":322},[309,2370,1551],{"class":314},[309,2372,2147],{"class":333},[309,2374,1542],{"class":314},[309,2376,1501],{"class":314},[309,2378,1528],{"class":322},[309,2380,1531],{"class":333},[309,2382,1534],{"class":322},[309,2384,1507],{"class":314},[309,2386,1539],{"class":393},[309,2388,1542],{"class":314},[309,2390,1528],{"class":322},[309,2392,1531],{"class":333},[309,2394,1534],{"class":322},[309,2396,1551],{"class":314},[309,2398,2399],{"class":333}," null",[309,2401,2402,2404,2406,2408,2410,2412,2414,2416],{"class":311,"line":1133},[309,2403,1559],{"class":314},[309,2405,1562],{"class":326},[309,2407,491],{"class":314},[309,2409,1567],{"class":322},[309,2411,1570],{"class":314},[309,2413,1270],{"class":314},[309,2415,800],{"class":318},[309,2417,1577],{"class":322},[309,2419,2420,2422,2424,2426],{"class":311,"line":1138},[309,2421,1582],{"class":314},[309,2423,1562],{"class":326},[309,2425,491],{"class":314},[309,2427,2428],{"class":322}," item;\n",[309,2430,2431],{"class":311,"line":69},[309,2432,448],{"emptyLinePlaceholder":245},[309,2434,2435,2437,2439,2441,2443,2445,2447,2449,2451,2453,2455,2457,2459,2461,2463],{"class":311,"line":1147},[309,2436,883],{"class":314},[309,2438,474],{"class":314},[309,2440,477],{"class":318},[309,2442,776],{"class":322},[309,2444,1453],{"class":318},[309,2446,337],{"class":322},[309,2448,779],{"class":318},[309,2450,898],{"class":322},[309,2452,483],{"class":318},[309,2454,405],{"class":322},[309,2456,816],{"class":326},[309,2458,491],{"class":314},[309,2460,909],{"class":322},[309,2462,912],{"class":318},[309,2464,915],{"class":322},[309,2466,2467],{"class":311,"line":244},[309,2468,920],{"class":322},[309,2470,2471],{"class":311,"line":1184},[309,2472,448],{"emptyLinePlaceholder":245},[309,2474,2475],{"class":311,"line":1189},[309,2476,448],{"emptyLinePlaceholder":245},[309,2478,2479,2481,2483,2485,2487],{"class":311,"line":1194},[309,2480,363],{"class":314},[309,2482,468],{"class":333},[309,2484,471],{"class":314},[309,2486,528],{"class":318},[309,2488,740],{"class":322},[309,2490,2491],{"class":311,"line":1213},[309,2492,2493],{"class":459},"\u002F\u002F ^ const dict: Map\u003CPerson, Person>",[299,2495,2498],{"className":1218,"code":2496,"filename":2497,"language":304,"meta":21,"style":21},"\u002F\u002F Apply what you've learned - add value parameter using the same pattern [!code highlight]\n\nexport function toMap\u003C\n T,\n KF extends keyof T | ((item: T) => any) | undefined,\n KV extends keyof T | ((item: T) => any) | undefined, \u002F\u002F [!code highlight]\n>(\n array: readonly T[],\n key?: KF,\n value?: KV, \u002F\u002F [!code highlight]\n) {\n type TKeyType = undefined extends KF ? T : KF extends keyof T ? T[KF] : KF extends ((item: T) => infer K) ? K : never;\n\n type TValueType = undefined extends KV \u002F\u002F [!code highlight]\n ? T \u002F\u002F [!code highlight]\n : KV extends ((item: T) => infer VF) \u002F\u002F [!code highlight]\n ? VF \u002F\u002F [!code highlight]\n : KV extends keyof T \u002F\u002F [!code highlight]\n ? T[KV] \u002F\u002F [!code highlight]\n : never; \u002F\u002F [!code highlight] \n\n if (!array?.length)\n return new Map\u003CTKeyType, TValueType>();\n\n const keyFn: (item: T) => TKeyType\n = typeof key === 'function'\n ? key\n : key !== undefined && typeof array[0] === 'object' && array[0] !== null\n ? item => item[key as keyof T]\n : item => item;\n\n const valueFn: (item: T) => TValueType \u002F\u002F [!code highlight]\n = typeof value === 'function' \u002F\u002F [!code highlight]\n ? value \u002F\u002F [!code highlight]\n : value !== undefined && typeof array[0] === 'object' && array[0] !== null \u002F\u002F [!code highlight]\n ? item => item[value as keyof T] \u002F\u002F [!code highlight]\n : item => item; \u002F\u002F [!code highlight]\n\n return new Map\u003CTKeyType, TValueType>(array.map(item => [keyFn(item), valueFn(item)]));\n}\n\nconst dict = toMap(data, 'key', 'birthday');\n\u002F\u002F ^ const dict: Map\u003Cnumber, Date> [!code highlight]\n","6",[306,2499,2500,2505,2510,2520,2526,2560,2596,2600,2612,2622,2635,2639,2714,2718,2734,2741,2770,2777,2790,2805,2814,2818,2832,2851,2855,2877,2889,2895,2931,2949,2959,2963,2987,3002,3010,3047,3068,3081,3086,3126,3131,3135,3157],{"__ignoreMap":21},[309,2501,2502],{"class":311,"line":20},[309,2503,2504],{"class":459},"\u002F\u002F Apply what you've learned - add value parameter using the same pattern",[309,2506,2508],{"class":2507,"line":131},[311,1231],[309,2509,448],{"emptyLinePlaceholder":245},[309,2511,2512,2514,2516,2518],{"class":311,"line":155},[309,2513,768],{"class":314},[309,2515,771],{"class":314},[309,2517,528],{"class":318},[309,2519,973],{"class":322},[309,2521,2522,2524],{"class":311,"line":180},[309,2523,978],{"class":318},[309,2525,1701],{"class":322},[309,2527,2528,2530,2532,2534,2536,2538,2540,2542,2544,2546,2548,2550,2552,2554,2556,2558],{"class":311,"line":204},[309,2529,1264],{"class":318},[309,2531,1267],{"class":314},[309,2533,1270],{"class":314},[309,2535,800],{"class":318},[309,2537,1275],{"class":314},[309,2539,813],{"class":322},[309,2541,816],{"class":326},[309,2543,330],{"class":314},[309,2545,800],{"class":318},[309,2547,823],{"class":322},[309,2549,826],{"class":314},[309,2551,1734],{"class":333},[309,2553,823],{"class":322},[309,2555,2144],{"class":314},[309,2557,2147],{"class":333},[309,2559,1701],{"class":322},[309,2561,2563,2566,2568,2570,2572,2574,2576,2578,2580,2582,2584,2586,2588,2590,2592,2594],{"class":2562,"line":445},[311,1231],[309,2564,2565],{"class":318}," KV",[309,2567,1267],{"class":314},[309,2569,1270],{"class":314},[309,2571,800],{"class":318},[309,2573,1275],{"class":314},[309,2575,813],{"class":322},[309,2577,816],{"class":326},[309,2579,330],{"class":314},[309,2581,800],{"class":318},[309,2583,823],{"class":322},[309,2585,826],{"class":314},[309,2587,1734],{"class":333},[309,2589,823],{"class":322},[309,2591,2144],{"class":314},[309,2593,2147],{"class":333},[309,2595,337],{"class":322},[309,2597,2598],{"class":311,"line":451},[309,2599,787],{"class":322},[309,2601,2602,2604,2606,2608,2610],{"class":311,"line":456},[309,2603,792],{"class":326},[309,2605,330],{"class":314},[309,2607,797],{"class":314},[309,2609,800],{"class":318},[309,2611,803],{"class":322},[309,2613,2614,2616,2618,2620],{"class":311,"line":463},[309,2615,1313],{"class":326},[309,2617,2173],{"class":314},[309,2619,1318],{"class":318},[309,2621,1701],{"class":322},[309,2623,2625,2628,2630,2633],{"class":2624,"line":41},[311,1231],[309,2626,2627],{"class":326}," value",[309,2629,2173],{"class":314},[309,2631,2632],{"class":318}," KV",[309,2634,337],{"class":322},[309,2636,2637],{"class":311,"line":610},[309,2638,837],{"class":322},[309,2640,2641,2643,2645,2647,2649,2651,2653,2656,2658,2661,2663,2665,2667,2669,2671,2673,2675,2677,2679,2681,2683,2685,2687,2689,2691,2693,2695,2697,2699,2701,2703,2706,2708,2710,2712],{"class":311,"line":616},[309,2642,1339],{"class":314},[309,2644,1342],{"class":318},[309,2646,471],{"class":314},[309,2648,2147],{"class":333},[309,2650,1267],{"class":314},[309,2652,1318],{"class":318},[309,2654,2655],{"class":314}," ?",[309,2657,800],{"class":318},[309,2659,2660],{"class":314}," 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*\u002F\n",[309,3248,3249,3251,3253,3255],{"class":311,"line":610},[309,3250,768],{"class":314},[309,3252,771],{"class":314},[309,3254,528],{"class":318},[309,3256,973],{"class":322},[309,3258,3259,3261],{"class":311,"line":616},[309,3260,978],{"class":318},[309,3262,1701],{"class":322},[309,3264,3265,3267,3269,3271,3273,3275,3277,3279,3281,3283,3285,3287,3289,3291,3293,3295],{"class":311,"line":621},[309,3266,1264],{"class":318},[309,3268,1267],{"class":314},[309,3270,1270],{"class":314},[309,3272,800],{"class":318},[309,3274,1275],{"class":314},[309,3276,813],{"class":322},[309,3278,816],{"class":326},[309,3280,330],{"class":314},[309,3282,800],{"class":318},[309,3284,823],{"class":322},[309,3286,826],{"class":314},[309,3288,1734],{"class":333},[309,3290,823],{"class":322},[309,3292,2144],{"class":314},[309,3294,2147],{"class":333},[309,3296,1701],{"class":322},[309,3298,3299,3301,3303,3305,3307,3309,3311,3313,3315,3317,3319,3321,3323,3325,3327,3329],{"class":311,"line":627},[309,3300,2565],{"class":318},[309,3302,1267],{"class":314},[309,3304,1270],{"class":314},[309,3306,800],{"class":318},[309,3308,1275],{"class":314},[309,3310,813],{"class":322},[309,3312,816],{"class":326},[309,3314,330],{"class":314},[309,3316,800],{"class":318},[309,3318,823],{"class":322},[309,3320,826],{"class":314},[309,3322,1734],{"class":333},[309,3324,823],{"class":322},[309,3326,2144],{"class":314},[309,3328,2147],{"class":333},[309,3330,1701],{"class":322},[309,3332,3333],{"class":311,"line":655},[309,3334,787],{"class":322},[309,3336,3337,3339,3341,3343,3345],{"class":311,"line":661},[309,3338,792],{"class":326},[309,3340,330],{"class":314},[309,3342,797],{"class":314},[309,3344,800],{"class":318},[309,3346,803],{"class":322},[309,3348,3349,3351,3353,3355],{"class":311,"line":666},[309,3350,1313],{"class":326},[309,3352,2173],{"class":314},[309,3354,1318],{"class":318},[309,3356,1701],{"class":322},[309,3358,3359,3361,3363,3365],{"class":311,"line":672},[309,3360,2627],{"class":326},[309,3362,2173],{"class":314},[309,3364,2632],{"class":318},[309,3366,1701],{"class":322},[309,3368,3369],{"class":311,"line":712},[309,3370,837],{"class":322},[309,3372,3373,3375,3377,3379,3381,3383,3385,3387,3389,3391,3393,3395,3397,3399,3401,3403,3405,3407,3409,3411,3413,3415,3417,3419,3421,3423,3425,3427,3429,3431,3433,3435,3437,3439,3441],{"class":311,"line":55},[309,3374,1339],{"class":314},[309,3376,1342],{"class":318},[309,3378,471],{"class":314},[309,3380,2147],{"class":333},[309,3382,1267],{"class":314},[309,3384,1318],{"class":318},[309,3386,2655],{"class":314},[309,3388,800],{"class":318},[309,3390,2660],{"class":314},[309,3392,1318],{"class":318},[309,3394,1267],{"class":314},[309,3396,1270],{"class":314},[309,3398,800],{"class":318},[309,3400,2655],{"class":314},[309,3402,800],{"class":318},[309,3404,1363],{"class":322},[309,3406,1366],{"class":318},[309,3408,1534],{"class":322},[309,3410,330],{"class":314},[309,3412,1318],{"class":318},[309,3414,1267],{"class":314},[309,3416,813],{"class":322},[309,3418,816],{"class":326},[309,3420,330],{"class":314},[309,3422,800],{"class":318},[309,3424,823],{"class":322},[309,3426,826],{"class":314},[309,3428,1833],{"class":314},[309,3430,829],{"class":318},[309,3432,823],{"class":322},[309,3434,2705],{"class":314},[309,3436,829],{"class":318},[309,3438,2660],{"class":314},[309,3440,1413],{"class":333},[309,3442,2280],{"class":322},[309,3444,3445,3447,3449,3451,3453,3455,3457,3459,3461,3463,3465,3467,3469,3471,3473,3475,3477,3479,3481,3483,3485,3487,3489,3491,3493,3495,3497,3499,3501,3503,3505,3507,3509,3511,3513],{"class":311,"line":722},[309,3446,1339],{"class":314},[309,3448,2725],{"class":318},[309,3450,471],{"class":314},[309,3452,2147],{"class":333},[309,3454,1267],{"class":314},[309,3456,2632],{"class":318},[309,3458,2655],{"class":314},[309,3460,800],{"class":318},[309,3462,2660],{"class":314},[309,3464,2632],{"class":318},[309,3466,1267],{"class":314},[309,3468,813],{"class":322},[309,3470,816],{"class":326},[309,3472,330],{"class":314},[309,3474,800],{"class":318},[309,3476,823],{"class":322},[309,3478,826],{"class":314},[309,3480,1833],{"class":314},[309,3482,2766],{"class":318},[309,3484,823],{"class":322},[309,3486,2705],{"class":314},[309,3488,2766],{"class":318},[309,3490,2660],{"class":314},[309,3492,2632],{"class":318},[309,3494,1267],{"class":314},[309,3496,1270],{"class":314},[309,3498,800],{"class":318},[309,3500,2655],{"class":314},[309,3502,800],{"class":318},[309,3504,1363],{"class":322},[309,3506,2801],{"class":318},[309,3508,1534],{"class":322},[309,3510,330],{"class":314},[309,3512,1413],{"class":333},[309,3514,2280],{"class":322},[309,3516,3517],{"class":311,"line":728},[309,3518,448],{"emptyLinePlaceholder":245},[309,3520,3521,3523,3525,3527,3529,3531],{"class":311,"line":743},[309,3522,842],{"class":314},[309,3524,845],{"class":322},[309,3526,848],{"class":314},[309,3528,851],{"class":322},[309,3530,854],{"class":333},[309,3532,2264],{"class":322},[309,3534,3535,35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TValueType\n",[309,3687,3688,3690,3692,3694,3696],{"class":311,"line":1189},[309,3689,1498],{"class":314},[309,3691,1501],{"class":314},[309,3693,2996],{"class":322},[309,3695,1507],{"class":314},[309,3697,1510],{"class":393},[309,3699,3700,3702],{"class":311,"line":1194},[309,3701,1515],{"class":314},[309,3703,3704],{"class":322}," value\n",[309,3706,3707,3709,3711,3713,3715,3717,3719,3721,3723,3725,3727,3729,3731,3733,3735,3737,3739],{"class":311,"line":1213},[309,3708,1523],{"class":314},[309,3710,2996],{"class":322},[309,3712,1551],{"class":314},[309,3714,2147],{"class":333},[309,3716,1542],{"class":314},[309,3718,1501],{"class":314},[309,3720,1528],{"class":322},[309,3722,1531],{"class":333},[309,3724,1534],{"class":322},[309,3726,1507],{"class":314},[309,3728,1539],{"class":393},[309,3730,1542],{"class":314},[309,3732,1528],{"class":322},[309,3734,1531],{"class":333},[309,3736,1534],{"class":322},[309,3738,1551],{"class":314},[309,3740,1554],{"class":333},[309,3742,3743,3745,3747,3749,3751,3753,3755,3757],{"class":311,"line":3071},[309,3744,1559],{"class":314},[309,3746,1562],{"class":326},[309,3748,491],{"class":314},[309,3750,3058],{"class":322},[309,3752,1570],{"class":314},[309,3754,1270],{"class":314},[309,3756,800],{"class":318},[309,3758,1577],{"class":322},[309,3760,3761,3763,3765,3767],{"class":311,"line":3083},[309,3762,1582],{"class":314},[309,3764,1562],{"class":326},[309,3766,491],{"class":314},[309,3768,2428],{"class":322},[309,3770,3771],{"class":311,"line":3088},[309,3772,448],{"emptyLinePlaceholder":245},[309,3774,3775],{"class":311,"line":3128},[309,3776,3777],{"class":459}," \u002F\u002F Create the map and loop the array only once\n",[309,3779,3780,3782,3785,3787,3789,3791,3793,3795,3797,3799],{"class":311,"line":265},[309,3781,1474],{"class":314},[309,3783,3784],{"class":333}," map",[309,3786,471],{"class":314},[309,3788,474],{"class":314},[309,3790,477],{"class":318},[309,3792,776],{"class":322},[309,3794,1453],{"class":318},[309,3796,337],{"class":322},[309,3798,2848],{"class":318},[309,3800,874],{"class":322},[309,3802,3803,3806,3809,3812,3814,3816,3818],{"class":311,"line":3137},[309,3804,3805],{"class":322}," array.",[309,3807,3808],{"class":318},"forEach",[309,3810,3811],{"class":322},"((",[309,3813,816],{"class":326},[309,3815,823],{"class":322},[309,3817,826],{"class":314},[309,3819,3820],{"class":322}," {\n",[309,3822,3823,3826,3829,3831,3833,3835,3837],{"class":311,"line":3159},[309,3824,3825],{"class":322}," map.",[309,3827,3828],{"class":318},"set",[309,3830,405],{"class":322},[309,3832,912],{"class":318},[309,3834,3119],{"class":322},[309,3836,3122],{"class":318},[309,3838,3839],{"class":322},"(item));\n",[309,3841,3843],{"class":311,"line":3842},44,[309,3844,3845],{"class":322}," });\n",[309,3847,3849],{"class":311,"line":3848},45,[309,3850,448],{"emptyLinePlaceholder":245},[309,3852,3854,3856],{"class":311,"line":3853},46,[309,3855,883],{"class":314},[309,3857,3858],{"class":322}," map;\n",[309,3860,3862],{"class":311,"line":3861},47,[309,3863,920],{"class":322},[309,3865,3867],{"class":311,"line":3866},48,[309,3868,448],{"emptyLinePlaceholder":245},[309,3870,3872,3874,3876,3878,3880,3882,3884,3886,3888,3890],{"class":311,"line":3871},49,[309,3873,363],{"class":314},[309,3875,468],{"class":333},[309,3877,471],{"class":314},[309,3879,528],{"class":318},[309,3881,531],{"class":322},[309,3883,534],{"class":393},[309,3885,337],{"class":322},[309,3887,488],{"class":326},[309,3889,491],{"class":314},[309,3891,943],{"class":322},[309,3893,3895],{"class":311,"line":3894},50,[309,3896,3897],{"class":459},"\u002F\u002F ^ const dict: Map\u003Cnumber, Date>\n",[231,3899,3900,3901,702],{},"Want to see how thoroughly this function is tested? Check out the full test file here ",[3902,3903,3907],"a",{"href":3904,"rel":3905},"https:\u002F\u002Fgithub.com\u002Fjeroenbach\u002Fbach.software\u002Fblob\u002Fmain\u002Fsrc\u002Fapp\u002Futils\u002FtoMap.test.ts",[3906],"nofollow","toMap.tests.ts",[3909,3910,3912],"h3",{"id":3911},"working-with-strictnullchecks-disabled","Working with strictNullChecks disabled",[231,3914,3915,3916,3918,3919,702],{},"When strictNullChecks is disabled (or strict mode itself is disabled), undefined becomes assignable to all types, which breaks our conditional type.\nIn this scenario, regardless of the parameters passed to ",[306,3917,505],{},", the resulting map will always have the key and value types ",[306,3920,779],{},[231,3922,3923],{},"To handle this limitation, you can use function overloads to provide explicit type signatures that correspond to the different parameter combinations, ensuring\ntype safety even when strict null checks ar disabled.",[231,3925,3926],{},"Here's how you can implement this:",[751,3928,3929],{},[299,3930,3932],{"className":301,"code":3931,"filename":3166,"language":304,"meta":21,"style":21},"\u002F**\n * Helps to create a map (dictionary) from a list of items.\n * For the key and values you can either provide a keyof T or a function that returns the value.\n * If you don't specify any value, the whole item will be used as value.\n *\n * @param array the array to convert\n * @param key a keyof an array item | a function that returns a value that represents the key of the dictionary\n * @param value a keyof an array item | a function that returns any value\n * @returns an new Map()\n *\u002F\nexport function toMap\u003CT>(array: readonly T[]): Map\u003CT, T>;\nexport function toMap\u003CT, KF extends keyof T>(\n array: readonly T[],\n key: KF,\n): Map\u003CT[KF], T>;\nexport function toMap\u003CT, KF extends (item: T) => any>(\n array: readonly T[],\n key: KF,\n): Map\u003CReturnType\u003CKF>, T>;\nexport function toMap\u003CT, KF extends keyof T, VF extends keyof T>(\n array: readonly T[],\n key: KF,\n value: VF,\n): Map\u003CT[KF], T[VF]>;\nexport function toMap\u003CT, KF extends keyof T, VF extends (item: T) => any>(\n array: readonly T[],\n key: KF,\n value: VF,\n): Map\u003CT[KF], ReturnType\u003CVF>>;\nexport function toMap\u003C\n T,\n KF extends (item: T) => any,\n VF extends (item: T) => any,\n>(\n array: readonly T[],\n key?: KF,\n value?: VF,\n): Map\u003CReturnType\u003CKF>, ReturnType\u003CVF>>;\nexport function toMap\u003CT, KF extends (item: T) => any, VF extends keyof T>(\n array: readonly T[],\n key: KF,\n value: VF,\n): Map\u003CReturnType\u003CKF>, T[VF]>;\n\nexport function toMap\u003C\n T,\n KF extends keyof T | ((item: T) => any) | undefined,\n KV extends keyof T | ((item: T) => any) | undefined,\n>(array: readonly T[], key?: KF, value?: KV) {\n type TKeyType = undefined extends KV\n ? T\n : KF extends keyof T\n ? T[KF]\n : KF extends (item: T) => infer K\n ? K\n : never;\n type TValueType = undefined extends KV\n ? T\n : KV extends (item: T) => infer VF\n ? VF\n : KV extends keyof T\n ? T[KV]\n : never;\n\n if (!array?.length) return new Map\u003CTKeyType, TValueType>();\n\n const keyFn: (item: T) => TKeyType =\n typeof key === 'function'\n ? key\n : key !== undefined && typeof array[0] === 'object' && array[0] !== null\n ? item => item[key as keyof T]\n : item => item;\n\n const valueFn: (item: T) => TValueType =\n typeof value === 'function'\n ? value\n : value !== undefined && typeof array[0] === 'object' && array[0] !== null\n ? item => item[value as keyof T]\n : item => item;\n\n \u002F\u002F Create the map and loop the array only once\n const map = new Map\u003CTKeyType, TValueType>();\n array?.forEach(item => {\n map.set(keyFn(item), valueFn(item));\n });\n\n return 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