{"id":120171,"date":"2022-02-14T06:00:32","date_gmt":"2022-02-13T21:00:32","guid":{"rendered":"https:\/\/anthem00.xsrv.jp\/2023_new_tcd\/?p=120171"},"modified":"2022-05-26T22:13:58","modified_gmt":"2022-05-26T13:13:58","slug":"javascript-null-undefined","status":"publish","type":"post","link":"https:\/\/anthem00.xsrv.jp\/2023_new_tcd\/2022\/02\/javascript-null-undefined.html","title":{"rendered":"\u3010JavaScript\u306e\u5165\u9580\u3011null\u578b\u30fbundefined\u578b"},"content":{"rendered":"

undefined\u578b\u3068null\u578b\u306f\u3001\u4ed6\u306e\u30d7\u30ea\u30df\u30c6\u30a3\u30d6\u306e\u30c7\u30fc\u30bf\u578b\u306b\u6bd4\u3079\u308b\u3068\u7279\u6b8a\u306a\u30c7\u30fc\u30bf\u578b\u3067\u3059\u3002\u3053\u308c\u3089\u304c\u6301\u3064\u5024\u306e\u610f\u5473\u306b\u7591\u554f\u3092\u6301\u3064\u65b9\u3082\u3044\u308b\u306e\u3067\u306f\u306a\u3044\u3067\u3057\u3087\u3046\u304b\u3002<\/p>\n

\u4eca\u56de\u306f\u3001\u305d\u306e\u3088\u3046\u306a\u7591\u554f\u3092\u89e3\u6d88\u3067\u304d\u308b\u3088\u3046\u306b\u3001undefined\u578b\u30fbnull\u578b\u3068\u306f\u4f55\u304b\u3001\u307e\u305f\u305d\u308c\u3089\u306e\u9055\u3044\u306b\u3064\u3044\u3066\u89e3\u8aac\u3057\u3066\u3044\u304d\u307e\u3059\u3002<\/p>\n

null\u578b<\/h2>\n

null\u578b\u306f\u3001\u5c11\u3057\u5909\u308f\u3063\u305f\u30c7\u30fc\u30bf\u578b\u3067\u3001\u81ea\u8eab\u306e\u300cnull\u300d\u3068\u3044\u3046\u5024\u306e\u307f\u3092\u6301\u3063\u3066\u3044\u307e\u3059\u3002
\nnull\u5024\u306b\u306f\u3001\u300c\u5024\u304c\u7a7a\u300d\u300c\u5024\u304c\u306a\u3044\u300d\u300c\u5024\u304c\u4e0d\u660e\u300d\u3068\u3044\u3046\u610f\u5473\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n

typeof\u6f14\u7b97\u5b50\u3092\u4f7f\u3063\u3066\u578b\u3092\u8abf\u3079\u308b\u3068\"object\"<\/code>\u304c\u8fd4\u3055\u308c\u307e\u3059\u3002<\/p>\n

\n
console.log(typeof null); \/\/ \"object\"\r\n<\/code><\/pre>\n<\/div>\n
\u3053\u3053\u3067\u300c\u306a\u305c\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\uff1f\u300d\u3068\u3044\u3046\u7591\u554f\u304c\u751f\u307e\u308c\u307e\u3059\u306d\u3002
\nnull\u304c\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3068\u5224\u5b9a\u3055\u308c\u308b\u306e\u306f\u3001\u516c\u5f0f\u306b\u8a8d\u3081\u3089\u308c\u3066\u3044\u308b\u8a00\u8a9e\u7684\u306a\u30a8\u30e9\u30fc\u3067\u3001\u4e92\u63db\u6027\u304c\u7dad\u6301\u3055\u308c\u3066\u3044\u307e\u3059\u3002
\n\u3064\u307e\u308a\u3001null\u306f\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3067\u306f\u306a\u304f\u3001\u5358\u306b\u8a00\u8a9e\u306e\u30a8\u30e9\u30fc\u306b\u3088\u3063\u3066\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3068\u5224\u5b9a\u3055\u308c\u3066\u3044\u308b\u3068\u3044\u3046\u3053\u3068\u3067\u3059\u3002<\/p>\n
null\u578b\u306f\u3001\u610f\u56f3\u7684\u306b\u5024\u304c\u5b58\u5728\u3057\u306a\u3044\u3053\u3068\u3092\u8868\u3057\u307e\u3059\u3002<\/p>\n
\n
let name = null;\r\nconsole.log(name); \/\/ null\r\n<\/code><\/pre>\n<\/div>\n
\u610f\u56f3\u7684\u306b\u3068\u3044\u3046\u70b9\u304c\u30dd\u30a4\u30f3\u30c8\u3067\u3001\u5909\u6570\u304c\u7279\u5b9a\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3084\u5024\u3092\u53c2\u7167\u3057\u3066\u3044\u306a\u3044\u3053\u3068\u3092\u793a\u3057\u305f\u308a\u3001\u30c7\u30fc\u30bf\u304c\u5b58\u5728\u3059\u308b\u304b\u78ba\u8a8d\u3059\u308b\u305f\u3081\u306b\u4f7f\u7528\u3055\u308c\u3066\u3044\u307e\u3059\u3002<\/p>\n
\u4f8b\u3048\u3070\u3001\u4ee5\u4e0b\u306e\u3088\u3046\u306a\u30b1\u30fc\u30b9\u3067\u3059\u3002
\nuser<\/code>\u3068\u3044\u3046\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306ename<\/code>\u30d7\u30ed\u30d1\u30c6\u30a3\u306b\u3001\u521d\u671f\u5024\u3068\u3057\u3066null<\/code>\u3092\u8a2d\u5b9a\u3057\u3066\u3044\u307e\u3059\u3002
\n\u307e\u305f\u3001if\u6587\u3092\u4f7f\u7528\u3057\u3066\u30c7\u30fc\u30bf\u304c\u7a7a\u3067\u3042\u308c\u3070\u300c\u30c7\u30fc\u30bf\u304c\u3042\u308a\u307e\u305b\u3093\u300d\u3068\u3044\u3046\u51e6\u7406\u3092\u884c\u3063\u3066\u3044\u307e\u3059\u3002<\/p>\n
\n
let user = {\r\n  name: null \/\/ \u5024\u304c\u7a7a\u3067\u3042\u308b\u3053\u3068\u3092\u660e\u793a\u3059\u308b\r\n}\r\n\r\nif (user.name === null) {\r\n  console.log('\u30c7\u30fc\u30bf\u304c\u3042\u308a\u307e\u305b\u3093')\r\n}\r\n\r\n\/\/ \"\u30c7\u30fc\u30bf\u304c\u3042\u308a\u307e\u305b\u3093\"\r\n<\/code><\/pre>\n<\/div>\n
\u3053\u306e\u3088\u3046\u306b\u30c7\u30fc\u30bf\u3042\u308b\u304b\u3069\u3046\u304b\u3092\u5224\u5b9a\u3057\u3001\u305d\u306e\u5224\u5b9a\u7d50\u679c\u306b\u3088\u3063\u3066\u51e6\u7406\u3092\u5206\u3051\u3066\u884c\u3046\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n
undefined\u578b<\/h2>\n
undefined\u578b\u3082\u3001null\u578b\u3068\u540c\u3058\u304f\u7279\u6b8a\u306a\u30c7\u30fc\u30bf\u578b\u3067\u3001\u81ea\u8eab\u306e\u300cundefined\u300d\u3068\u3044\u3046\u5024\u306e\u307f\u3092\u6301\u3063\u3066\u3044\u307e\u3059\u3002
\nundefined\u5024\u306b\u306f\u3001\u300c\u5024\u304c\u672a\u5b9a\u7fa9\u300d\u300c\u5024\u304c\u4ee3\u5165\u3055\u308c\u3066\u3044\u306a\u3044\u300d\u3068\u3044\u3046\u610f\u5473\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n
typeof\u6f14\u7b97\u5b50\u3092\u4f7f\u3063\u3066\u578b\u3092\u8abf\u3079\u308b\u3068\"undefined\"<\/code>\u304c\u8fd4\u3055\u308c\u307e\u3059\u3002<\/p>\n
\n
console.log(typeof undefined); \/\/ \"undefined\"\r\n<\/code><\/pre>\n<\/div>\n
\u5909\u6570\u306f\u5ba3\u8a00\u3055\u308c\u3066\u3044\u308b\u304c\u5024\u304c\u4ee3\u5165\u3055\u308c\u3066\u3044\u306a\u3044\u5834\u5408\u3001\u305d\u306e\u5024\u306fundefined<\/code>\u3068\u306a\u308a\u307e\u3059\u3002<\/p>\n
\n
let name;\r\nconsole.log(name); \/\/ undefined\r\n<\/code><\/pre>\n<\/div>\n
\u6280\u8853\u7684\u306b\u306fundefined\u578b\u3082null\u578b\u3068\u540c\u3058\u3088\u3046\u306b\u3001\u5909\u6570\u306bundefined<\/code>\u306e\u5024\u3092\u4ee3\u5165\u3059\u308b\u3053\u3068\u306f\u53ef\u80fd\u3067\u3059\u3002<\/p>\n
\n
let name = undefined;\r\nconsole.log(name); \/\/ undefined\r\n<\/code><\/pre>\n<\/div>\n
\u3057\u304b\u3057\u3001\u3053\u306e\u65b9\u6cd5\u306f\u3042\u307e\u308a\u63a8\u5968\u3055\u308c\u3066\u3044\u307e\u305b\u3093\u3002
\nundefined\u578b\u306f\u3001\u5909\u6570\u304c\u5272\u308a\u5f53\u3066\u3089\u308c\u3066\u3044\u308b\u304b\u3001\u305d\u3046\u3067\u306a\u3044\u304b\u78ba\u8a8d\u3059\u308b\u305f\u3081\u306b\u4f7f\u308f\u308c\u3066\u3044\u308b\u304b\u3089\u3067\u3059\u3002
\n\u610f\u56f3\u7684\u306b\u5024\u304c\u7a7a\u3067\u3042\u308b\u3053\u3068\u3092\u660e\u793a\u3059\u308b\u306b\u5834\u5408\u306b\u306f\u3001null\u578b\u3092\u4f7f\u3046\u306e\u304c\u4e00\u822c\u7684\u3067\u3059\u3002<\/p>\n
null\u3068undefined\u306e\u9055\u3044<\/h2>\n
null\u3068undefined\u306f\u3001\u3069\u3061\u3089\u3082\u300c\u5024\u304c\u306a\u3044\u300d\u3053\u3068\u3092\u610f\u5473\u3059\u308b\u70b9\u306f\u5171\u901a\u3057\u3066\u3044\u307e\u3059\u3002
\n\u610f\u5473\u5408\u3044\u7684\u306a\u9055\u3044\u306f\u3001null\u306f\u300c\u5024\u81ea\u4f53\u304c\u5b58\u5728\u3057\u306a\u3044\u305f\u3081\u3001\u5024\u304c\u306a\u3044\u300d\u3001undefined\u306f\u300c\u5024\u304c\u4ee3\u5165\u3055\u308c\u3066\u3044\u306a\u3044\u305f\u3081\u3001\u5024\u304c\u306a\u3044\u300d\u3068\u3044\u3046\u30a4\u30e1\u30fc\u30b8\u3067\u3059\u3002<\/p>\n
\u5b9f\u969b\u306b\u306f\u3053\u308c\u3089\u306e\u610f\u5473\u3092\u53b3\u5bc6\u306b\u7406\u89e3\u3057\u4f7f\u3044\u5206\u3051\u308b\u306e\u306f\u3001\u73fe\u5f79\u306e\u30d7\u30ed\u30b0\u30e9\u30de\u30fc\u3067\u3082\u304b\u3093\u305f\u3093\u3067\u306f\u3042\u308a\u307e\u305b\u3093\u3002
\n\u300cnull\u3092\u4f7f\u3046\u3079\u304d\u3060\u300d\u3001\u300cundefined\u3092\u4f7f\u3046\u3079\u304d\u3060\u300d\u3068\u3044\u3046\u8ad6\u70b9\u3068\u306a\u308b\u30c6\u30fc\u30de\u3060\u304b\u3089\u3067\u3059\u3002<\/p>\n
\u305d\u306e\u305f\u3081\u3001\u3053\u3053\u3067\u306f\u610f\u5473\u5408\u3044\u7684\u306a\u9055\u3044\u3067\u306f\u306a\u304f\u3001JavaScript\u306e\u8a00\u8a9e\u4e0a\u3067\u306e\u4ed5\u69d8\u306e\u9055\u3044\u3092\u898b\u3066\u3044\u304d\u307e\u3059\u3002<\/p>\n
\u81ea\u7136\u767a\u751f\u3059\u308b\u304b\/\u3057\u306a\u3044\u304b<\/h3>\n
null\u306f\u3001\u660e\u793a\u7684\u306b\u4f7f\u308f\u306a\u3044\u9650\u308a\u3001\u81ea\u7136\u306b\u767a\u751f\u3059\u308b\u3082\u306e\u3067\u306f\u3042\u308a\u307e\u305b\u3093\u3002
\n\u53cd\u5bfe\u306b\u3001undefined\u306f\u3001\u660e\u793a\u7684\u306b\u4f7f\u308f\u306a\u304f\u3066\u3082\u3001\u5024\u304c\u4ee3\u5165\u3055\u308c\u3066\u3044\u306a\u3044\u5834\u5408\u306b\u306f\u3001\u81ea\u7136\u306b\u767a\u751f\u3057\u3066\u304d\u307e\u3059\u3002<\/p>\n
\n
let name1 = null; \/\/\u3000null\u3092\u660e\u793a\u3057\u3066\u3044\u308b\r\nconsole.log(name1); \/\/ null\r\n\r\nlet name2; \/\/ undefined\u3092\u660e\u793a\u3057\u3066\u3044\u308b\u308f\u3051\u3067\u306f\u306a\u3044\r\nconsole.log(name2); \/\/ undefined\r\n<\/code><\/pre>\n<\/div>\n
\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306b\u5b58\u5728\u3057\u306a\u3044\u30d7\u30ed\u30d1\u30c6\u30a3\u306b\u30a2\u30af\u30bb\u30b9\u3057\u305f\u969b\u306b\u3082\u3001undefined<\/code>\u304c\u8fd4\u308a\u307e\u3059\u3002<\/p>\n
\n
let user = {\r\n  name: 'John'\r\n}\r\n\r\nconsole.log(user.name); \/\/ \"John\" \u2192 name\u30d7\u30ed\u30d1\u30c6\u30a3\u306f\u5b58\u5728\u3059\u308b\r\nconsole.log(user.age); \/\/ undefined \u2192 age\u30d7\u30ed\u30d1\u30c6\u30a3\u306f\u5b58\u5728\u3057\u306a\u3044\r\n<\/code><\/pre>\n<\/div>\n
\u65e2\u306b\u4ee3\u5165\u3055\u308c\u3066\u3044\u305f\u3068\u601d\u3063\u3066\u3044\u305f\u5024\u306b\u30a2\u30af\u30bb\u30b9\u3057\u305f\u3068\u3053\u308d\u3001undefined<\/code>\u304c\u8fd4\u3063\u3066\u304d\u3066\u3001\u30b9\u30da\u30eb\u30df\u30b9\u304c\u539f\u56e0\u3060\u3063\u305f\u3053\u3068\u306b\u6c17\u304c\u4ed8\u304f\u3053\u3068\u3082\u3042\u308a\u307e\u3059\u3002<\/p>\n
\n
let fruits = ['apple', 'banana', 'blueberry'];\r\nconsole.log(fruit); \/\/ fruit is not defined\" \u2192 fruit\u3067\u306f\u306a\u304f\u3066fruits\uff08\u8907\u6570\u5f62\uff09\r\n<\/code><\/pre>\n<\/div>\n
\u3053\u306e\u3088\u3046\u306bundefined\u306f\u81ea\u7136\u767a\u751f\u3059\u308b\u305f\u3081\u3001\u898b\u304b\u3051\u308b\u983b\u5ea6\u3082\u591a\u304f\u306a\u308a\u307e\u3059\u3002<\/p>\n
typeof\u6f14\u7b97\u5b50<\/h3>\n
\u3055\u3044\u3054\u306b\u30c7\u30fc\u30bf\u578b\u306e\u9055\u3044\u306b\u3064\u3044\u3066\u5fa9\u7fd2\u3057\u3066\u304a\u304d\u307e\u3057\u3087\u3046\u3002
\ntypeof\u6f14\u7b97\u5b50\u3067\u30c7\u30fc\u30bf\u578b\u3092\u8abf\u3079\u308b\u3068\u3001null\u306f\"object\"<\/code>\u3067\u3042\u308b\u306e\u306b\u5bfe\u3057\u3001undefined\u306f\"undefined\"<\/code>\u304c\u8fd4\u308a\u307e\u3059\u3002<\/p>\n
\n
console.log(typeof null); \/\/ \"object\"\r\nconsole.log(typeof undefined); \/\/ \"undefined\"\r\n<\/code><\/pre>\n<\/div>\n
\u307e\u3068\u3081<\/h2>\n
\u4eca\u56de\u306f\u3001null\u578b\u3068undefined\u578b\u306b\u3064\u3044\u3066\u89e3\u8aac\u3057\u307e\u3057\u305f\u3002
\nnull\u3068undefined\u306f\u7406\u89e3\u3057\u306b\u304f\u3044\u5074\u9762\u3082\u3042\u308a\u307e\u3059\u304c\u3001\u305d\u308c\u3089\u306e\u5024\u306f\u30d7\u30ed\u30b0\u30e9\u30e0\u306e\u3069\u3053\u306b\u6319\u52d5\u304c\u8d77\u3053\u3063\u3066\u3044\u308b\u306e\u304b\u30d2\u30f3\u30c8\u306b\u306a\u308a\u307e\u3059\u3002<\/p>\n
\u307e\u305a\u306f\u304b\u3093\u305f\u3093\u306a\u7279\u5fb4\u3092\u63b4\u3093\u3067\u3044\u304d\u307e\u3057\u3087\u3046\u3002<\/p>\n
\n
\/\/ \u30dd\u30a4\u30f3\u30c8\r\n* null\u578b\u306f\u3001\u610f\u56f3\u3092\u6301\u3063\u3066null\u3092\u4ee3\u5165\u3057\u3066\u5024\u304c\u306a\u3044\u3053\u3068\u3092\u793a\u3059\r\n* undefined\u578b\u306f\u3001\u5024\u304c\u4ee3\u5165\u3055\u308c\u3066\u3044\u306a\u3044\u305f\u3081\u5024\u304c\u306a\u3044\u3053\u3068\u304c\u793a\u3055\u308c\u308b<\/code><\/pre>\n<\/div>\n
\u5408\u308f\u305b\u3066\u8aad\u307f\u305f\u3044\u30c7\u30fc\u30bf\u578b\u5165\u9580\u30b7\u30ea\u30fc\u30ba<\/h2>\n
\u7b2c1\u56de\uff1a\u30c7\u30fc\u30bf\u578b\u3068typeof\u6f14\u7b97\u5b50<\/strong><\/a>
\n\u7b2c2\u56de\uff1a\u30c7\u30fc\u30bf\u578b -\u30d7\u30ea\u30df\u30c6\u30a3\u30d6<\/strong><\/a>
\n\u7b2c3\u56de\uff1a\u30c7\u30fc\u30bf\u578b -\u30aa\u30d6\u30b8\u30a7\u30af\u30c8<\/strong><\/a>
\n\u7b2c4\u56de\uff1a\u6587\u5b57\u5217\u578b\uff08String\uff09<\/strong><\/a>
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