\u3010JavaScript\u5165\u9580\u3011undefined\u5fb9\u5e95\u89e3\u8aac\uff01\u4f7f\u3044\u65b9\u3084\u5224\u5b9a\u65b9\u6cd5\u307e\u3068\u3081<\/div>\n
\u66f4\u65b0\u65e5\uff1a2024\u5e745\u67086\u65e5<\/div>\n <\/div>\n <\/div>\n <\/div>\n <\/a>\n \n
\u300cnull\u300d\u306e\u4ee3\u5165\u306b\u3064\u3044\u3066<\/h2>\n\u5909\u6570\u306bnull\u3092\u4ee3\u5165\u3057\u305f\u6642\u306e\u6319\u52d5\u306b\u3064\u3044\u3066<\/h3>\n
null\u3092\u5909\u6570\u306b\u4ee3\u5165\u3059\u308b\u3068\u305d\u306e\u5f8c\u3001\u5909\u6570\u306f\u3069\u306e\u3088\u3046\u306b\u8a55\u4fa1\u3055\u308c\u308b\u306e\u3067\u3057\u3087\u3046\u304b\u3002\u5909\u6570\u3068null\u3084undefined\u3068\u306e\u95a2\u4fc2\u306f\u3069\u306e\u3088\u3046\u306a\u3082\u306e\u3067\u3057\u3087\u3046\u304b\u3002<\/p>\n
\u5b9f\u969b\u306b\u30b3\u30fc\u30c9\u3067\u78ba\u8a8d\u3057\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n
window.onload = function () {\r\n \/\/ null\u3092\u4ee3\u5165\u3057\u30c1\u30a7\u30c3\u30af\u3059\u308b\r\n var val = null;\r\n console.log('val == null : ' + (val == null));\r\n console.log('val === null : ' + (val === null));\r\n console.log('val == undefined : ' + (val == undefined));\r\n console.log('val === undedfined : ' + (val === undefined));\r\n}<\/pre>\n\u5b9f\u884c\u7d50\u679c\uff1a<\/p>\n
val == null : true\r\nval === null : true\r\nval == undefined : true\r\nval === undedfined : false<\/pre>\n\u4ee5\u4e0a\u306e\u3088\u3046\u306b\u3001\u5909\u6570\u306bnull\u3092\u4ee3\u5165\u3059\u308b\u3068\u3001\u305d\u306e\u5f8c\u305d\u306e\u5909\u6570\u306f\u3001null\u3068\u540c\u7b49\u306a\u6271\u3044\u306b\u306a\u308a\u307e\u3059\u3002\u3064\u307e\u308a\u3001\u5909\u6570\u306fnull\u3068\u3057\u3066\u632f\u308b\u821e\u3044\u307e\u3059\u3002<\/p>\n
\u5909\u6570\u306bundefined\u3092\u4ee3\u5165\u3057\u305f\u6642\u306e\u6319\u52d5\u306b\u3064\u3044\u3066<\/h3>\n
undefined\u3092\u5909\u6570\u306b\u4ee3\u5165\u3059\u308b\u3068\u305d\u306e\u5f8c\u3001\u5909\u6570\u306f\u3069\u306e\u3088\u3046\u306b\u8a55\u4fa1\u3055\u308c\u308b\u306e\u3067\u3057\u3087\u3046\u304b\u3002\u5909\u6570\u3068null\u3084undefined\u3068\u306e\u95a2\u4fc2\u306f\u3069\u306e\u3088\u3046\u306a\u3082\u306e\u3067\u3057\u3087\u3046\u304b\u3002<\/p>\n
window.onload = function () {\r\n \/\/ undefined\u3092\u4ee3\u5165\u3057\u30c1\u30a7\u30c3\u30af\u3059\u308b\r\n var val = undefined;\r\n console.log('val == undefined : ' + (val == undefined));\r\n console.log('val === undedfined : ' + (val === undefined));\r\n console.log('val == null : ' + (val == null));\r\n console.log('val === null : ' + (val === null));\r\n}<\/pre>\n\u5b9f\u884c\u7d50\u679c\uff1a<\/p>\n
val == undefined : true\r\nval === undedfined : true\r\nval == null : true\r\nval === null : false<\/pre>\n\u4ee5\u4e0a\u306e\u3088\u3046\u306b\u3001\u5909\u6570\u306bundefined\u3092\u4ee3\u5165\u3059\u308b\u3068\u3001\u305d\u306e\u5f8c\u305d\u306e\u5909\u6570\u306f\u3001undefined\u3068\u540c\u7b49\u306a\u6271\u3044\u306b\u306a\u308a\u307e\u3059\u3002\u3064\u307e\u308a\u3001\u5909\u6570\u306fundefined\u3068\u3057\u3066\u632f\u308b\u821e\u3044\u307e\u3059<\/b>\u3002<\/p>\n\u914d\u5217\u306bnull\u3092\u4ee3\u5165\u3059\u308b\u65b9\u6cd5<\/h3>\n
\u6b21\u306b\u3001\u914d\u5217\u30c7\u30fc\u30bf\u3078\u300cnull\u300d\u3092\u4ee3\u5165\u3059\u308b\u65b9\u6cd5\u306b\u3064\u3044\u3066\u898b\u3066\u3044\u304d\u307e\u3057\u3087\u3046\uff01<\/p>\n
\u914d\u5217\u306e\u5834\u5408\u3082\u5358\u7d14\u306a\u5909\u6570\u306e\u6642\u3068\u540c\u3058\u3067\u3059\u304c\u3001\u5c11\u3057\u6027\u8cea\u304c\u7570\u306a\u308b\u90e8\u5206\u3082\u3042\u308a\u307e\u3059\u3002\u4f8b\u3048\u3070\u6b21\u306e\u30b5\u30f3\u30d7\u30eb\u4f8b\u3092\u898b\u3066\u304f\u3060\u3055\u3044\uff01<\/p>\n
var items = [];\r\n\r\nconsole.log( items[0] );<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
undefined<\/pre>\n\u3053\u306e\u4f8b\u3067\u306f\u3001\u914d\u5217\u300citems\u300d\u3092\u5ba3\u8a00\u3057\u3066\u540c\u6642\u306b\u521d\u671f\u5316\u3092\u884c\u3063\u3066\u3044\u308b\u306e\u304c\u5206\u304b\u308a\u307e\u3059\u3002<\/p>\n
\u3053\u306e\u72b6\u614b\u3067\u914d\u5217\u306e0\u756a\u76ee\u3092\u898b\u3066\u307f\u308b\u3068\u3001\u3059\u3067\u306bundefined\u306b\u306a\u3063\u3066\u3044\u308b\u306e\u304c\u5206\u304b\u308a\u307e\u3059\u3002\u914d\u5217\u306e\u5834\u5408\u306f\u3001\u30ea\u30c6\u30e9\u30eb\u3067\u521d\u671f\u5316\u3057\u3066\u3044\u3066\u3082\u5024\u306f\u5b9a\u7fa9\u3055\u308c\u3066\u3044\u306a\u3044\u306e\u3067\u3084\u306f\u308aundefined\u306b\u306a\u308b\u308f\u3051\u3067\u3059\u3002<\/p>\n
\u3053\u306e\u521d\u671f\u5316\u3068\u540c\u6642\u306b\u300cnull\u300d\u3092\u4f7f\u3063\u3066\u4ee3\u5165\u3059\u308b\u3068\u6b21\u306e\u3088\u3046\u306b\u306a\u308a\u307e\u3059\uff01<\/p>\n
var items = [ null, null, null ];\r\n\r\nconsole.log( items[0] );<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
null<\/pre>\n\u3053\u306e\u4f8b\u3067\u306f\u3001\u521d\u671f\u5316\u3059\u308b\u969b\u306b3\u3064\u306enull\u3092\u4ee3\u5165\u3057\u3066\u3044\u308b\u306e\u3067\u7a7a\u306e\u30c7\u30fc\u30bf3\u500b\u5206\u306e\u914d\u5217\u304c\u4f5c\u3089\u308c\u305f\u308f\u3051\u3067\u3059\u3002\u914d\u5217\u30c7\u30fc\u30bf\u304cnull\u306b\u306a\u3063\u3066\u3044\u308b\u306e\u306f\u5b9f\u884c\u7d50\u679c\u304b\u3089\u3082\u5206\u304b\u308a\u307e\u3059\u306d\u3002<\/p>\n
OR\u3092\u4f7f\u3063\u305fnull\u306e\u4ee3\u5165\u65b9\u6cd5<\/h3>\n
\u300cnull\u300d\u306f\u8ad6\u7406\u6f14\u7b97\u5b50\u306e\u300cOR\u300d\u3092\u4f7f\u3063\u305f\u4ee3\u5165\u65b9\u6cd5\u3082\u3088\u304f\u4f7f\u308f\u308c\u308b\u306e\u3067\u89e3\u8aac\u3057\u3066\u304a\u304d\u307e\u3059\uff01<\/p>\n
OR\u6f14\u7b97\u5b50\u306f\u3001\u8907\u6570\u306e\u6761\u4ef6\u304b\u30891\u3064\u3060\u3051\u5f53\u3066\u306f\u307e\u308b\u969b\u306b\u51e6\u7406\u3092\u884c\u3044\u305f\u3044\u5834\u5408\u306b\u3088\u304f\u4f7f\u308f\u308c\u307e\u3059\u3002\u4eca\u56de\u306e\u5834\u5408\u3060\u3068\u3001\u4efb\u610f\u306e\u5909\u6570\u306b\u5024\u304c\u7121\u304b\u3063\u305f\u5834\u5408\u306b\u521d\u671f\u5024\u3068\u3057\u3066\u300cnull\u300d\u3092\u81ea\u52d5\u7684\u306b\u4ee3\u5165\u3059\u308b\u30b1\u30fc\u30b9\u3067\u4f7f\u308f\u308c\u307e\u3059\u3002<\/p>\n
\u6b21\u306e\u30b5\u30f3\u30d7\u30eb\u4f8b\u3092\u898b\u3066\u304f\u3060\u3055\u3044\uff01<\/p>\n
var item;\r\n\r\nvar result = item || null;\r\n\r\nconsole.log( result );<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
null<\/pre>\n\u3053\u306e\u5834\u5408\u3001\u5909\u6570\u300citem\u300d\u306f\u5ba3\u8a00\u3055\u308c\u305f\u3060\u3051\u3067\u300c\u5024\u300d\u306f\u4ee3\u5165\u3055\u308c\u3066\u3044\u307e\u305b\u3093\u3088\u306d\uff1f<\/p>\n
\u3053\u306e\u3088\u3046\u306a\u72b6\u6cc1\u3067\u300citem || null\u300d\u3068\u8a18\u8ff0\u3059\u308b\u3068\u3001\u81ea\u52d5\u7684\u306b\u521d\u671f\u5024\u3068\u3057\u3066\u300cnull\u300d\u304c\u4ee3\u5165\u3055\u308c\u308b\u308f\u3051\u3067\u3059\u3002\u3082\u3061\u308d\u3093\u3001\u4f55\u3089\u304b\u306e\u5024\u304c\u3059\u3067\u306b\u4ee3\u5165\u3055\u308c\u3066\u3044\u308c\u3070\u300cnull\u300d\u306f\u4ee3\u5165\u3055\u308c\u307e\u305b\u3093\u3002<\/p>\n
\u307e\u305f\u3001\u521d\u671f\u5024\u304c\u300cnull\u300d\u3060\u3063\u305f\u5834\u5408\u306b\u4f55\u3089\u304b\u306e\u300c\u5024\u300d\u3092\u4ee3\u5165\u3057\u305f\u3044\u30b1\u30fc\u30b9\u306b\u3082\u5229\u7528\u3067\u304d\u307e\u3059\uff01<\/p>\n
var item = null;\r\n\r\nvar result = item || 100;<\/pre>\n\u3053\u306e\u4f8b\u3067\u306f\u3001\u521d\u671f\u5024\u3068\u3057\u3066\u5909\u6570\u300citem\u300d\u306bnull\u304c\u4ee3\u5165\u3055\u308c\u3066\u3044\u307e\u3059\u3002\u3053\u306e\u5834\u5408\u3082\u300cundefined\u300d\u3068\u540c\u69d8\u306b\u521d\u671f\u5024\u3068\u3057\u3066\u300c100\u300d\u304c\u81ea\u52d5\u7684\u306b\u4ee3\u5165\u3055\u308c\u308b\u308f\u3051\u3067\u3059\u3002<\/p>\n
\u300cnull\u300d\u306e\u5909\u63db\u306b\u3064\u3044\u3066<\/h2>\nnull\u3092Boolean\u578b\u306e\u5909\u6570\u306b\u5909\u63db\u3059\u308b<\/h3>\n
null\u3092Boolean\u578b\u306b\u5909\u63db\u3059\u308b\u3068\u3001\u3069\u306e\u3088\u3046\u306a\u5024\u306b\u306a\u308b\u306e\u3067\u3057\u3087\u3046\u304b\u3002<\/p>\n
\u5b9f\u969b\u306b\u30b3\u30fc\u30c9\u3067\u78ba\u8a8d\u3057\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n
console.log('Boolean(null) = ' + Boolean(null));\r\n<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
Boolean(null) = false\r\n<\/pre>\nnull\u3092Boolean\u578b\u306b\u5909\u63db\u3059\u308b\u3068\u3001\u5024\u306ffalse\u306b\u306a\u308a\u307e\u3057\u305f\u3002\u3053\u308c\u306fif\u306a\u3069\u306e\u6761\u4ef6\u5f0f\u3078null\u3092\u6e21\u3057\u305f\u969b\u306bfalse\u3068\u8a55\u4fa1\u3055\u308c\u305f\u6642\u3068\u540c\u3058\u7d50\u679c\u306b\u306a\u3063\u3066\u3044\u307e\u3059\u3002<\/p>\n
\u3064\u307e\u308a\u3001null\u306f\u300c\u5024\u304c\u5b58\u5728\u3057\u306a\u3044\u300d\u3068\u3044\u3046\u610f\u5473\u3067\u3059\u304b\u3089\u3001if\u306a\u3069\u3067\u8a55\u4fa1\u3055\u308c\u305f\u969b\u306b\u306f\u5426\u5b9a\u7684\u306a\u8a55\u4fa1\u306b\u306a\u308b\u306e\u3067false\u3068\u540c\u7b49<\/b>\u3067\u3042\u308b\u308f\u3051\u3067\u3059\u3002<\/p>\nnull\u3092\u6587\u5b57\u5217\u578b\u306e\u5909\u6570\u306b\u5909\u63db\u3059\u308b<\/h3>\n
null\u3092\u6587\u5b57\u5217\u578b\uff08String\u578b\uff09\u306b\u5909\u63db\u3059\u308b\u3068\u3001\u3069\u306e\u3088\u3046\u306a\u5024\u306b\u306a\u308b\u306e\u3067\u3057\u3087\u3046\u304b\u3002\u5b9f\u969b\u306b\u30b3\u30fc\u30c9\u3067\u78ba\u8a8d\u3057\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n
console.log('String(null) = ' + String(null));\r\nconsole.log('String(null) == null : ' + (String(null) == null));\r\n<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
String(null) = null\r\nString(null) == null : false\r\n<\/pre>\nnull\u3092\u6587\u5b57\u5217\u578b\u306b\u5909\u63db\u3059\u308b\u3068\u3001\u300cnull\u300d\u3068\u3044\u3046\u6587\u5b57\u5217\u306b\u306a\u308a\u307e\u3057\u305f\u3002<\/p>\n
\u3053\u308c\u306fJavaScript\u306e\u6587\u5b57\u5217\u578b\u306e\u7279\u6b8a\u6a5f\u80fd\u3067\u3001null\u3092\u6587\u5b57\u5217\u578b\u306b\u5909\u63db\u3059\u308b\u969b\u306b\u5024\u304cnull\u3067\u3042\u3063\u305f\u3053\u3068\u304c\u308f\u304b\u308b\u3088\u3046\u306b\u300cnull\u300d\u3068\u3044\u3046\u6587\u5b57\u5217\u306b\u5909\u63db\u3057\u3066\u3044\u308b\u305f\u3081\u3067\u3059\u3002<\/p>\n
\u5909\u63db\u7d50\u679c\u304c\u3042\u304f\u307e\u3067\u6587\u5b57\u5217\u3067\u3042\u308a\u3001null\u3068\u306f\u4e00\u81f4\u3057\u3066\u3044\u306a\u3044\u3053\u3068\u306f\u4e0a\u8a18\u5b9f\u884c\u7d50\u679c\u306e\u901a\u308a\u3067\u3059\u3002<\/p>\n
null\u3092Number\u578b\u306e\u5909\u6570\u306b\u5909\u63db\u3059\u308b<\/h3>\n
null\u3092Number\u578b\u306b\u5909\u63db\u3059\u308b\u3068\u3001\u3069\u306e\u3088\u3046\u306a\u5024\u306b\u306a\u308b\u306e\u3067\u3057\u3087\u3046\u304b\u3002\u5b9f\u969b\u306b\u30b3\u30fc\u30c9\u3067\u78ba\u8a8d\u3057\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n
console.log('Number(null) = ' + Number(null));\r\n<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
Number(null) = 0\r\n<\/pre>\nnull\u3092Number\u578b\u306b\u5909\u63db\u3059\u308b\u30680\u3068\u3044\u3046\u5024\u306b\u306a\u308a\u307e\u3057\u305f\u30020\u306fNumber\u578b\u3067\u300c\uff08\u3042\u304f\u307e\u3067Number\u578b\u306e\u6570\u5024\u8a08\u7b97\u306b\u304a\u3044\u3066\uff09\u5024\u304c\u5b58\u5728\u3057\u306a\u3044\u300d\u3068\u3044\u3046\u610f\u5473\u3067\u3059\u3002<\/p>\n
null\u3082\u300c\u5024\u304c\u5b58\u5728\u3057\u306a\u3044\u300d\u3068\u3044\u3046\u610f\u5473\u3067\u3042\u308b\u3053\u3068\u304b\u3089\u3001\u5408\u7406\u7684\u306a\u5909\u63db\u7d50\u679c\u3067\u3059\u3002<\/p>\n
\u300cnull\u300d\u306e\u5224\u5b9a\u306b\u3064\u3044\u3066<\/h2>\nnull\u3068undefined\u3092\u5224\u5b9a\u3059\u308b<\/h3>\n
\u307e\u305a\u6700\u521d\u306b\u3001null\u3068\u3088\u304f\u4e00\u7dd2\u306b\u6271\u308f\u308c\u308bundefined\u3092\u305d\u308c\u305e\u308c\u3069\u306e\u3088\u3046\u306b\u5224\u5b9a\u3059\u308c\u3070\u826f\u3044\u306e\u304b\u3092\u898b\u3066\u3044\u304d\u307e\u3057\u3087\u3046\u3002<\/p>\n
\u3068\u8a00\u3063\u3066\u3082\u65b9\u6cd5\u306f\u7c21\u5358\u3067\u3001\u57fa\u672c\u7684\u306b\u306f\u300cnull\u300d\u300cundefined\u300d\u305d\u308c\u305e\u308c\u3092\u540c\u3058\u5024\u3067\u5224\u5b9a<\/b>\u3059\u308c\u3070\u554f\u984c\u306f\u3042\u308a\u307e\u305b\u3093\u3002<\/p>\nvar n = null;\r\nvar u = undefined;\r\n\r\nconsole.log(n === null);\r\nconsole.log(u === undefined);\r\n<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
true\r\ntrue\r\n<\/pre>\n\u3053\u306e\u7d50\u679c\u3092\u5fdc\u7528\u3059\u308c\u3070\u3001\u6b21\u306e\u3088\u3046\u306a\u6761\u4ef6\u5206\u5c90\u51e6\u7406\u304c\u66f8\u3051\u307e\u3059\u306d\u3002<\/p>\n
if(hoge === null || hoge === undefined) { }\r\n<\/pre>\n\u3053\u308c\u3067\u5909\u6570\u300choge\u300d\u306e\u4e2d\u306b\u300cnull\u300d\u304b\u300cundefined\u300d\u304c\u683c\u7d0d\u3055\u308c\u3066\u3044\u308c\u3070\u3001\u7d50\u679c\u306f\u300ctrue\u300d\u306b\u306a\u308b\u3068\u3044\u3046\u308f\u3051\u3067\u3059\u3002\u305f\u3060\u3057\u3001undefined\u306f\u30ed\u30fc\u30ab\u30eb\u5909\u6570\u3068\u3057\u3066\u4e0a\u66f8\u304d\u3067\u304d\u3066\u3057\u307e\u3046\u306e\u3067\u3001typeof\u3092\u4f7f\u3063\u305f\u5224\u5b9a\u306e\u65b9\u304c\u3088\u308a\u5b89\u5fc3\u3067\u3057\u3087\u3046\u3002<\/p>\n
if(hoge === null || typeof hoge === 'undefined') { }\r\n<\/pre>\nnull\u3092Boolean\u578b\u306e\u5909\u6570\u3068\u5224\u5b9a\u3059\u308b<\/h3>\n
null\u3068Boolean\u578b\u306etrue\u3084false\u3092\u3001\u6bd4\u8f03\u6f14\u7b97\u5b50==\u3084!=\u306a\u3069\u3067\u6bd4\u8f03\u3059\u308b\u3068\u3069\u3044\u3046\u7d50\u679c\u306b\u306a\u308b\u306e\u3067\u3057\u3087\u3046\u304b\u3002<\/p>\n
\u5b9f\u969b\u306b\u3001\u30b3\u30fc\u30c9\u3067\u6bd4\u8f03\u3057\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n
console.log('true === null : ' + (true === null));\r\nconsole.log('true !== null : ' + (true !== null));\r\nconsole.log('false === null : ' + (false === null));\r\nconsole.log('false !== null : ' + (false !== null));\r\n<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
true === null : false\r\ntrue !== null : true\r\nfalse === null : false\r\nfalse !== null : true\r\n<\/pre>\n\u4ee5\u4e0a\u306e\u3088\u3046\u306b\u3001Boolean\u578b\u306etrue\u3082false\u3082null\u3068\u306f\u5024\u3082\u578b\u3082\u307e\u3063\u305f\u304f\u9055\u3046\u3068\u3044\u3046\u6271\u3044\u3067\u3059\u3002<\/p>\n
true\u3084false\u306f\u610f\u5473\u306e\u3042\u308b\u5024\u304c\u3042\u308a\u3001\u300c\u5024\u304c\u306a\u3044\u300dnull\u3068\u306f\u9055\u3046\u305f\u3081\u3067\u3059\u3002\u305f\u3060\u3057\u3001null\u3092if\u6587\u306a\u3069\u306e\u6761\u4ef6\u5f0f\u3068\u3057\u3066\u4f7f\u7528\u3059\u308b\u969b\u3001\u4ee5\u4e0b\u306e\u30b3\u30fc\u30c9\u306e\u3088\u3046\u306b\u6271\u308f\u308c\u307e\u3059\u3002<\/p>\n
if (null) {\r\n console.log(\"if(null) : true\");\r\n} else {\r\n console.log(\"if(null) : false\");\r\n}\r\nif (!null) {\r\n console.log(\"if(!null) : true\");\r\n} else {\r\n console.log(\"if(!null) : false\");\r\n}\r\n<\/pre>\n\u4ee5\u4e0a\u306e\u3088\u3046\u306b\u3001if\u6587\u306a\u3069\u306e\u6761\u4ef6\u5f0f\u306bnull\u3092\u4e0e\u3048\u308b\u3068false\u3068\u540c\u7b49\u306e\u8a55\u4fa1\u3092\u3055\u308c\u307e\u3059\u3002<\/p>\n
null\u3092\u6587\u5b57\u5217\u578b\u306e\u5909\u6570\u3068\u5224\u5b9a\u3059\u308b<\/h3>\n
null\u3068\u3001\u6587\u5b57\u5217\u578b\u3092\u6bd4\u8f03\u6f14\u7b97\u5b50==\u3084===\u3067\u6bd4\u8f03\u3059\u308b\u3068\u3069\u3046\u306a\u308b\u3067\u3057\u3087\u3046\u304b\u3002\u5b9f\u969b\u306b\u3001\u30b3\u30fc\u30c9\u3067\u78ba\u8a8d\u3057\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n
console.log('\"\" === null : ' + (\"\" === null));\r\nconsole.log('\"0\" === null : ' + (\"0\" === null));\r\nconsole.log('\"A\" === null : ' + (\"A\" === null));\r\nconsole.log('\"abc\" === null : ' + (\"abc\" === null));\r\n<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
\"\" === null : false\r\n\"0\" === null : false\r\n\"A\" === null : false\r\n\"abc\" === null : false\r\n<\/pre>\n\u4ee5\u4e0a\u306e\u3088\u3046\u306b\u3001\u6587\u5b57\u5217\u306f\u3044\u305a\u308c\u3082null\u3068\u306f\u5024\u3082\u578b\u3082\u4e00\u81f4\u3057\u307e\u305b\u3093\u3002<\/p>\n
null\u3092Number\u578b\u306e\u5909\u6570\u3068\u5224\u5b9a\u3059\u308b<\/h3>\n
null\u3068\u3001Number\u578b\u3092\u6bd4\u8f03\u6f14\u7b97\u5b50==\u3084===\u3067\u6bd4\u8f03\u3059\u308b\u3068\u3069\u3046\u306a\u308b\u3067\u3057\u3087\u3046\u304b\u3002<\/p>\n
\u5b9f\u969b\u306b\u3001\u30b3\u30fc\u30c9\u3067\u78ba\u8a8d\u3057\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n
console.log('0 === null : ' + (0 === null));\r\nconsole.log('0.0 === null : ' + (0.0 === null));\r\nconsole.log('1 === null : ' + (1 === null));\r\nconsole.log('1.0 === null : ' + (1.0 === null));\r\nconsole.log('NaN === null : ' + (NaN === null));\r\nconsole.log('Inifity === null : ' + (Infinity === null));\r\n<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
0 === null : false\r\n0.0 === null : false\r\n1 === null : false\r\n1.0 === null : false\r\nNaN === null : false\r\nInifity === null : false\r\n<\/pre>\n\u4ee5\u4e0a\u306e\u3088\u3046\u306b\u3001Number\u578b\u306e\u5024\u306f\u3044\u305a\u308c\u3082null\u3068\u306f\u5024\u3082\u578b\u3082\u4e00\u81f4\u3057\u307e\u305b\u3093\u3002<\/p>\n
0\u306fnull\u3068\u5024\u304c\u4e00\u81f4\u3057\u305d\u3046\u3067\u3059\u304c\u3001\u300c\u6570\u5024\u306e0\u3068\u3044\u3046\u5024\u304c\u5b58\u5728\u3059\u308b\u300d\u3068\u3044\u3046\u610f\u5473\u3067\u3042\u308a\u3001null\u306f\u300c\u5024\u304c\u5b58\u5728\u3057\u306a\u3044\u300d\u3068\u3044\u3046\u610f\u5473\u306a\u306e\u3067\u4e00\u81f4\u3057\u307e\u305b\u3093\u3002\u307e\u305f\u3001\u975e\u6570\u5024\u3067\u3042\u308b\u3053\u3068\u3092\u793a\u3059NaN\uff08Not a Number\uff09\u3082null\u3068\u306f\u5024\u3082\u578b\u3082\u4e00\u81f4\u3057\u3066\u3044\u307e\u305b\u3093\u3002<\/p>\n
NaN\u306f\u300c\u975e\u6570\u5024\u3068\u3044\u3046\u3053\u3068\u3092\u793a\u3059\u5024<\/b>\u300d\u3060\u304b\u3089\u3067\u3059\u3002<\/p>\n\u95a2\u6570\u306b\u304a\u3051\u308bnull\u306e\u6ce8\u610f\u70b9<\/h2>\n
\u6700\u5f8c\u306b\u3001\u95a2\u6570\u3067\u300cnull\u300d\u3092\u6271\u3046\u969b\u306e\u6ce8\u610f\u70b9\u306b\u3064\u3044\u3066\u89e3\u8aac\u3057\u3066\u304a\u304d\u307e\u3059\uff01\u4f8b\u3048\u3070\u3001\u4f55\u3089\u304b\u306e\u5024\u3092\u5f15\u6570\u306b\u53d6\u308b\u95a2\u6570\u3092\u4f5c\u6210\u3059\u308b\u3068\u3057\u307e\u3059\u3002<\/p>\n
function sample(value) {\r\n var item = value || 100;\r\n\r\n console.log( item );\r\n}\r\n\r\nsample();<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
100<\/pre>\n\u3053\u306e\u4f8b\u3067\u306f\u30011\u3064\u306e\u5f15\u6570\u3092\u53d6\u308b\u95a2\u6570\u300csample\u300d\u3092\u4f5c\u6210\u3057\u3066\u3044\u307e\u3059\u3002sample()\u3092\u5b9f\u884c\u3059\u308b\u969b\u306b\u5f15\u6570\u3092\u6307\u5b9a\u3057\u306a\u304b\u3063\u305f\u5834\u5408\u306f\u3001\u300c||\u300d\u3092\u4f7f\u3063\u3066\u521d\u671f\u5024\u306b\u300c100\u300d\u3092\u4ee3\u5165\u3059\u308b\u3088\u3046\u306b\u3057\u3066\u3044\u307e\u3059\u306d\u3002<\/p>\n
\u305f\u3060\u3057\u3001\u610f\u56f3\u7684\u306b\u300cnull\u300d\u3092\u6307\u5b9a\u3057\u305f\u3044\u5834\u5408\u3082\u3042\u308a\u307e\u3059\u3002\u305d\u3053\u3067\u3001\u300csample( null )\u300d\u3068\u8a18\u8ff0\u3057\u3066\u521d\u671f\u5024\u3092\u300cnull\u300d\u306b\u3057\u305f\u3044\u3068\u601d\u3063\u3066\u3082\u3001\u7d50\u679c\u306f\u300c100\u300d\u306b\u306a\u3063\u3066\u3057\u307e\u3046\u308f\u3051\u3067\u3059\u3002<\/p>\n
\u3053\u306e\u3088\u3046\u306a\u30b1\u30fc\u30b9\u3067\u306f\u3001\u300c\u5f15\u6570\u3092\u6307\u5b9a\u3057\u306a\u304b\u3063\u305f\u5834\u5408 \uff1d undefined\u300d\u3068\u3044\u3046\u6027\u8cea\u3092\u5229\u7528\u3059\u308b\u3068\u4e0a\u624b\u304f\u52d5\u4f5c\u3057\u307e\u3059<\/b>\u3002<\/p>\n
\u6b21\u306e\u30b5\u30f3\u30d7\u30eb\u4f8b\u3092\u898b\u3066\u304f\u3060\u3055\u3044\uff01<\/p>\n
function sample(value) {\r\n var item = value;\r\n\r\n if(value === undefined) item = 100;\r\n\r\n console.log( item );\r\n}\r\n\r\nsample( null );<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
null<\/pre>\n\u3053\u306e\u4f8b\u3067\u306f\u3001\u5148\u307b\u3069\u3068\u540c\u3058\u95a2\u6570\u300csample()\u300d\u3092\u4f5c\u6210\u3057\u3001\u305d\u306e\u4e2d\u8eab\u306b\u300cundefined\u300d\u3068\u6bd4\u8f03\u3059\u308b\u6761\u4ef6\u5f0f\u3092\u8ffd\u52a0\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n
\u3053\u306e\u3088\u3046\u306b\u3001\u610f\u56f3\u7684\u306b\u300cundefined\u300d\u3068\u6bd4\u8f03\u3059\u308b\u3053\u3068\u3067\u5f15\u6570\u304c\u7121\u304b\u3063\u305f\u5834\u5408\u306b\u521d\u671f\u5024\u300c100\u300d\u304c\u4ee3\u5165\u3055\u308c\u308b\u308f\u3051\u3067\u3059\u3002\u3053\u308c\u306a\u3089\u95a2\u6570\u306e\u5f15\u6570\u306b\u300cnull\u300d\u3092\u6307\u5b9a\u3057\u3066\u3082\u3001\u5b9f\u884c\u7d50\u679c\u306e\u3088\u3046\u306b\u3057\u3063\u304b\u308a\u3068\u300cnull\u300d\u304c\u4ee3\u5165\u3067\u304d\u307e\u3059\uff01<\/p>\n
null\u306e\u4f7f\u3044\u65b9\u307e\u3068\u3081<\/h2>\n
\u6700\u5f8c\u306b\u3001null\u306e\u57fa\u672c\u7684\u306a\u4f7f\u3044\u65b9\u3084\u6982\u5ff5\u306b\u3064\u3044\u3066\u307e\u3068\u3081\u3066\u304a\u304d\u307e\u3059\u3002null\u306f\u300c\u7a7a\u3063\u307d\u300d\u306e\u72b6\u614b\u3092\u610f\u5473\u3059\u308b\u306e\u3067\u3001\u5909\u6570\u3084\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e\u30d7\u30ed\u30d1\u30c6\u30a3\u3092\u521d\u671f\u5316\u3059\u308b\u6642\u306b\u3088\u304f\u4f7f\u308f\u308c\u307e\u3059\u3002<\/p>\n
var item = null;\r\n\r\nvar obj = {\r\n name: null\r\n}\r\n<\/pre>\n\u3088\u304f\u4e00\u7dd2\u306b\u6271\u308f\u308c\u308bundefined\u3082\u4f3c\u3066\u3044\u308b\u306e\u3067\u3059\u304c\u3001\u3053\u3061\u3089\u306f\u300c\u672a\u5b9a\u7fa9\u3067\u3042\u308b\u300d\u3053\u3068\u3092\u610f\u5473\u3059\u308b\u3082\u306e\u306a\u306e\u3067\u6271\u3044\u3068\u3057\u3066\u306f\u5225\u7269\u306b\u306a\u308a\u307e\u3059\u3002\u4f8b\u3048\u3070\u3001\u4e21\u8005\u3092\u6bd4\u8f03\u3057\u3066\u307f\u308b\u3068\u6b21\u306e\u3088\u3046\u306b\u306a\u308a\u307e\u3059\u3002<\/p>\n
console.log( null == undefined );\r\nconsole.log( null === undefined );\r\n<\/pre>\n\u5b9f\u884c\u7d50\u679c<\/p>\n
true\r\nfalse\r\n<\/pre>\n\u666e\u901a\u306b\u300c==\u300d\u3067\u6bd4\u8f03\u3059\u308b\u3068\u540c\u3058\u3068\u5224\u5b9a\u3055\u308c\u307e\u3059\u304c\u3001\u300c===(\u53b3\u5bc6\u7b49\u4fa1\u6f14\u7b97\u5b50)\u300d\u3067\u6bd4\u8f03\u3059\u308b\u3068false\u3068\u306a\u308a\u578b\u304c\u9055\u3046\u306e\u3067\u5225\u7269\u306b\u306a\u308b\u308f\u3051\u3067\u3059\u3002\u307e\u305f\u3001null\u304bundefined\u306a\u306e\u304b\u3092\u5224\u5b9a\u3059\u308b\u306b\u306f\u6b21\u306e\u3088\u3046\u306a\u6761\u4ef6\u5206\u5c90\u3067\u884c\u3048\u307e\u3059\u3002<\/p>\n
if(hoge === null || hoge === undefined) { }\r\n<\/pre>\n\u5224\u5b9a\u3059\u308b\u5909\u6570\u300choge\u300d\u306b\u5bfe\u3057\u3066\u3001\u305d\u306e\u307e\u307enull\u304bundefined\u306a\u306e\u304b\u3092\u6bd4\u8f03\u3059\u308b\u3060\u3051\u3067\u826f\u3044\u308f\u3051\u3067\u3059\u3002<\/p>\n
\u307e\u3068\u3081<\/h2>\n
\u4eca\u56de\u306f\u3001\u300cnull\u300d\u3068\u300cundefined\u300d\u306e\u610f\u5473\u304b\u3089\u5224\u5b9a\u3001\u5909\u63db\u3001\u4ee3\u5165\u306b\u3064\u3044\u3066\u5b66\u7fd2\u3057\u307e\u3057\u305f\uff01<\/p>\n
\u5b66\u7fd2\u306e\u30dd\u30a4\u30f3\u30c8\u3092\u632f\u308a\u8fd4\u3063\u3066\u307f\u307e\u3057\u3087\u3046\uff01<\/p>\n
\n
\n- null\u306f\u300c\u5024\u304c\u5b58\u5728\u3057\u306a\u3044\u300d\u3001undefined\u306f\u300c\u5024\u304c\u672a\u5b9a\u7fa9\u300d\u3068\u3044\u3046\u610f\u5473<\/b><\/li>\n
- null\u3068undefined\u3092\u6587\u5b57\u5217\u306a\u3069\u3068\u6bd4\u8f03\u3059\u308b\u3068\u5408\u7406\u7684\u306a\u6bd4\u8f03\u7d50\u679c\u3068\u306a\u308b<\/b><\/li>\n
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