{"id":1136,"date":"2025-02-07T12:56:05","date_gmt":"2025-02-07T03:56:05","guid":{"rendered":"https:\/\/route-zero.com\/recruit\/route\/1136\/"},"modified":"2025-04-08T09:39:29","modified_gmt":"2025-04-08T00:39:29","slug":"1136","status":"publish","type":"route","link":"https:\/\/route-zero.com\/recruit\/route\/1136\/","title":{"rendered":"JavaScript\u4e2d\u7d1a\u8005\u3078\u306e\u30b9\u30c6\u30c3\u30d7\u30a2\u30c3\u30d7\uff5c\u5b9f\u52d9\u3067\u4f7f\u3048\u308b\u30c6\u30af\u30cb\u30c3\u30af10\u9078"},"content":{"rendered":"<div>\n<h2>JavaScript\u306e\u58c1<\/h2>\n<p>JavaScript\u3092\u66f8\u304d\u59cb\u3081\u3066\u3057\u3070\u3089\u304f\u7d4c\u3063\u305f\u9803\u3001\u3053\u3093\u306a\u58c1\u306b\u3076\u3064\u304b\u308b\u3053\u3068\u306f\u3042\u308a\u307e\u305b\u3093\u304b\uff1f<\/p>\n<ul>\n<li>\n<p>\u300c\u306a\u3093\u3068\u306a\u304f\u52d5\u304f\u30b3\u30fc\u30c9\u300d\u306f\u66f8\u3051\u308b\u3051\u3069\u3001\u3082\u3063\u3068\u52b9\u7387\u7684\u306b\u66f8\u304d\u305f\u3044<\/p>\n<\/li>\n<li>\n<p>\u53ef\u8aad\u6027\u306e\u9ad8\u3044\u30b3\u30fc\u30c9\u306b\u3057\u305f\u3044\u3051\u3069\u3001\u3069\u3053\u304b\u3089\u624b\u3092\u3064\u3051\u308c\u3070\u3044\u3044\u304b\u5206\u304b\u3089\u306a\u3044<\/p>\n<\/li>\n<li>\n<p>\u30c1\u30fc\u30e0\u958b\u767a\u3067\u6c42\u3081\u3089\u308c\u308b\u201c\u4e2d\u7d1a\u8005\u30ec\u30d9\u30eb\u201d\u306e\u30b9\u30ad\u30eb\u3063\u3066\u4f55\uff1f<\/p>\n<\/li>\n<\/ul>\n<p>\u672c\u8a18\u4e8b\u3067\u306f\u3001\u305d\u3093\u306a\u7591\u554f\u3092\u62b1\u3048\u308b\u3042\u306a\u305f\u306b\u5411\u3051\u3066\u3001\u5b9f\u52d9\u3067\u672c\u5f53\u306b\u5f79\u7acb\u3064\u201c\u4e2d\u7d1a\u8005\u5411\u3051JavaScript\u30c6\u30af\u30cb\u30c3\u30af\u201d\u309210\u500b\u53b3\u9078\u3057\u3066\u304a\u5c4a\u3051\u3057\u307e\u3059\u3002<\/p>\n<p>\u3059\u3079\u3066\u5b9f\u969b\u306b\u8a66\u305b\u308b\u30b3\u30fc\u30c9\u4ed8\u304d\u3067\u3001\u300c\u306a\u308b\u307b\u3069\u3001\u3053\u3046\u3059\u308c\u3070\u826f\u304b\u3063\u305f\u306e\u304b\uff01\u300d\u3068\u601d\u3048\u308b\u5185\u5bb9\u306b\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n<hr>\n<h2>\u5b9f\u52d9\u3067\u5dee\u304c\u3064\u304f\uff01\u4e2d\u7d1a\u8005\u5411\u3051JavaScript\u30c6\u30af\u30cb\u30c3\u30af10\u9078<\/h2>\n<h3>1. \u5206\u5272\u4ee3\u5165\u3067\u30b3\u30fc\u30c9\u3092\u7c21\u6f54\u306b<\/h3>\n<pre><code><span>\/\/ Before<\/span>\r\n<span>const<\/span> name = user.name;\r\n<span>const<\/span> age = user.age;\r\n\r\n<span>\/\/ After<\/span>\r\n<span>const<\/span> { name, age } = user;<\/code><\/pre>\n<p>\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u304b\u3089\u30d7\u30ed\u30d1\u30c6\u30a3\u3092\u53d6\u308a\u51fa\u3059\u3068\u304d\u3001\u5206\u5272\u4ee3\u5165\uff08Destructuring\uff09\u3092\u4f7f\u3048\u3070\u3001\u8aad\u307f\u3084\u3059\u304f\u30df\u30b9\u3082\u6e1b\u308a\u307e\u3059\u3002<\/p>\n<h3>2. Nullish Coalescing\u3067\u5b89\u5168\u306a\u5024\u51e6\u7406<\/h3>\n<pre><code><span>const<\/span> displayName = user.name ?? <span>'\u533f\u540d\u30e6\u30fc\u30b6\u30fc'<\/span>;<\/code><\/pre>\n<p>|| \u3068\u9055\u3063\u3066 null \u3084 undefined \u306e\u307f\u3092\u5bfe\u8c61\u306b\u3059\u308b\u305f\u3081\u30010\u3084\u7a7a\u6587\u5b57\u3092\u8aa4\u3063\u3066\u5224\u5b9a\u3059\u308b\u3053\u3068\u304c\u3042\u308a\u307e\u305b\u3093\u3002<\/p>\n<h3>3. Optional Chaining\u3067\u30cd\u30b9\u30c8\u306e\u6df1\u3044\u5024\u3082\u5b89\u5168\u306b\u30a2\u30af\u30bb\u30b9<\/h3>\n<pre><code><span>const<\/span> zipcode = user?.address?.zipcode;<\/code><\/pre>\n<p>\u30cd\u30b9\u30c8\u304c\u6df1\u3044\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e\u30a2\u30af\u30bb\u30b9\u3067\u3082\u30a8\u30e9\u30fc\u3092\u9632\u3052\u307e\u3059\u3002<\/p>\n<h3>4. \u30a2\u30ed\u30fc\u95a2\u6570\u3068this\u306e\u6271\u3044<\/h3>\n<pre><code><span>\/\/ \u901a\u5e38\u306e\u95a2\u6570\uff08this\u304c\u5909\u308f\u308b\uff09<\/span>\r\nsetTimeout(<span><span>function<\/span>(<span><\/span>) <\/span>{\r\n  <span>console<\/span>.log(<span>this<\/span>); <span>\/\/ Window<\/span>\r\n}, <span>1000<\/span>);\r\n\r\n<span>\/\/ \u30a2\u30ed\u30fc\u95a2\u6570\uff08this\u304c\u30ec\u30ad\u30b7\u30ab\u30eb\uff09<\/span>\r\nsetTimeout(<span><span>()<\/span> =&gt;<\/span> {\r\n  <span>console<\/span>.log(<span>this<\/span>); <span>\/\/ \u5916\u5074\u306ethis\u3092\u4fdd\u6301<\/span>\r\n}, <span>1000<\/span>);<\/code><\/pre>\n<p>this\u306e\u6271\u3044\u3067\u6df7\u4e71\u3057\u305f\u3053\u3068\u306f\u3042\u308a\u307e\u305b\u3093\u304b\uff1f\u30a2\u30ed\u30fc\u95a2\u6570\u306fthis\u304c\u56fa\u5b9a\u3055\u308c\u308b\u306e\u3067\u3001\u30a4\u30d9\u30f3\u30c8\u3084\u975e\u540c\u671f\u51e6\u7406\u3067\u3082\u4f7f\u3044\u3084\u3059\u3044\u3067\u3059\u3002<\/p>\n<h3>5. \u30b9\u30d7\u30ec\u30c3\u30c9\u69cb\u6587\u306e\u6d3b\u7528<\/h3>\n<pre><code><span>const<\/span> arr1 = [<span>1<\/span>, <span>2<\/span>];\r\n<span>const<\/span> arr2 = [<span>3<\/span>, <span>4<\/span>];\r\n<span>const<\/span> all = [...arr1, ...arr2]; <span>\/\/ [1,2,3,4]<\/span><\/code><\/pre>\n<p>\u914d\u5217\u306e\u7d50\u5408\u3084\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e\u30b3\u30d4\u30fc\u304c\u7c21\u5358\u306b\u306a\u308a\u307e\u3059\u3002<\/p>\n<h3>6. \u30c6\u30f3\u30d7\u30ec\u30fc\u30c8\u30ea\u30c6\u30e9\u30eb\u3067\u53ef\u8aad\u6027\u5411\u4e0a<\/h3>\n<pre><code><span>const<\/span> message = <span>`\u3053\u3093\u306b\u3061\u306f\u3001<span>${user.name}<\/span>\u3055\u3093\uff01`<\/span>;<\/code><\/pre>\n<p>\u8907\u96d1\u306a\u6587\u5b57\u5217\u9023\u7d50\u3082\u30c6\u30f3\u30d7\u30ec\u30fc\u30c8\u30ea\u30c6\u30e9\u30eb\u3067\u30b7\u30f3\u30d7\u30eb\u306b\u3002<\/p>\n<h3>7. \u9ad8\u968e\u95a2\u6570\uff08map\/filter\/reduce\uff09\u306e\u4f7f\u3044\u3053\u306a\u3057<\/h3>\n<pre><code><span>const<\/span> prices = [<span>100<\/span>, <span>200<\/span>, <span>300<\/span>];\r\n<span>const<\/span> withTax = prices.map(<span><span>p<\/span> =&gt;<\/span> p * <span>1.1<\/span>);<\/code><\/pre>\n<p>\u95a2\u6570\u578b\u30d7\u30ed\u30b0\u30e9\u30df\u30f3\u30b0\u306e\u7b2c\u4e00\u6b69\u3002\u696d\u52d9\u306e\u30c7\u30fc\u30bf\u6574\u5f62\u306b\u3082\u983b\u51fa\u3057\u307e\u3059\u3002<\/p>\n<h3>8. \u975e\u540c\u671f\u51e6\u7406\u306fasync\/await\u3067\u30b9\u30c3\u30ad\u30ea<\/h3>\n<pre><code><span>async<\/span> <span><span>function<\/span> <span>fetchData<\/span>(<span><\/span>) <\/span>{\r\n  <span>const<\/span> res = <span>await<\/span> fetch(<span>'\/api\/data'<\/span>);\r\n  <span>const<\/span> data = <span>await<\/span> res.json();\r\n  <span>console<\/span>.log(data);\r\n}<\/code><\/pre>\n<p>async \u3068 await \u306f\u3001JavaScript\u306b\u304a\u3051\u308b\u975e\u540c\u671f\u51e6\u7406\u3092\u3088\u308a\u76f4\u611f\u7684\u306b\u66f8\u304f\u305f\u3081\u306e\u69cb\u6587\u3067\u3059\u3002<\/p>\n<ul>\n<li>\n<p>async \u306f\u95a2\u6570\u3092\u975e\u540c\u671f\u95a2\u6570\u3068\u3057\u3066\u5b9a\u7fa9\u3059\u308b\u305f\u3081\u306e\u30ad\u30fc\u30ef\u30fc\u30c9\u3067\u3059\u3002\u3053\u306e\u95a2\u6570\u306f\u5e38\u306b Promise \u3092\u8fd4\u3057\u307e\u3059\u3002<\/p>\n<\/li>\n<li>\n<p>await \u306f\u3001async \u95a2\u6570\u306e\u4e2d\u3067\u4f7f\u3044\u3001Promise\u306e\u5b8c\u4e86\u3092\u5f85\u3064\u69cb\u6587\u3067\u3059\u3002<\/p>\n<\/li>\n<\/ul>\n<p>\u3053\u308c\u306b\u3088\u308a\u3001\u975e\u540c\u671f\u51e6\u7406\u3092\u540c\u671f\u51e6\u7406\u306e\u3088\u3046\u306b\u8a18\u8ff0\u3067\u304d\u3001\u30cd\u30b9\u30c8\u304c\u6df1\u304f\u306a\u308a\u304c\u3061\u306a Promise.then() \u30c1\u30a7\u30fc\u30f3\u3088\u308a\u3082\u8aad\u307f\u3084\u3059\u304f\u3001\u30a8\u30e9\u30fc\u30cf\u30f3\u30c9\u30ea\u30f3\u30b0\u3082\u3057\u3084\u3059\u3044\u30b3\u30fc\u30c9\u304c\u66f8\u3051\u307e\u3059\u3002<\/p>\n<h3>9. \u30a4\u30df\u30e5\u30fc\u30bf\u30d6\u30eb\u306a\u914d\u5217\u64cd\u4f5c<\/h3>\n<pre><code><span>const<\/span> newList = [...oldList, newItem];<\/code><\/pre>\n<p>\u72b6\u614b\u7ba1\u7406\u3067\u306f\u300c\u5143\u306e\u914d\u5217\u3092\u58ca\u3055\u306a\u3044\u300d\u66f8\u304d\u65b9\u304c\u6c42\u3081\u3089\u308c\u307e\u3059\u3002<\/p>\n<h3>10. \u30af\u30ea\u30fc\u30f3\u30b3\u30fc\u30c9\u306e\u610f\u8b58\uff08\u95a2\u6570\u5206\u5272\u30fb\u547d\u540d\uff09<\/h3>\n<pre><code><span><span>function<\/span> <span>calcTax<\/span>(<span>price<\/span>) <\/span>{\r\n  <span>return<\/span> price * <span>1.1<\/span>;\r\n}\r\n\r\n<span><span>function<\/span> <span>showPriceWithTax<\/span>(<span>price<\/span>) <\/span>{\r\n  <span>const<\/span> taxed = calcTax(price);\r\n  <span>console<\/span>.log(<span>`\u7a0e\u8fbc\u4fa1\u683c\u306f<span>${taxed}<\/span>\u5186\u3067\u3059\u3002`<\/span>);\r\n}<\/code><\/pre>\n<p>\u3072\u3068\u3064\u306e\u95a2\u6570\u306b\u8907\u6570\u306e\u8cac\u4efb\u3092\u6301\u305f\u305b\u305a\u3001\u610f\u56f3\u304c\u660e\u78ba\u306b\u306a\u308b\u3088\u3046\u5206\u5272\u3059\u308b\u306e\u304c\u30dd\u30a4\u30f3\u30c8\u3067\u3059\u3002<\/p>\n<hr>\n<h2>\u3088\u304f\u3042\u308b\u843d\u3068\u3057\u7a74\u3068\u6539\u5584\u30dd\u30a4\u30f3\u30c8<\/h2>\n<h3>\u843d\u3068\u3057\u7a741\uff1aundefined\u306e\u307e\u307e\u64cd\u4f5c\u3057\u3066\u30a8\u30e9\u30fc<\/h3>\n<pre><code><span>\/\/ NG<\/span>\r\n<span>const<\/span> <span>len<\/span> = user.name.length; <span>\/\/ name\u304cundefined\u3060\u3068\u30a8\u30e9\u30fc<\/span>\r\n\r\n<span>\/\/ OK<\/span>\r\n<span>const<\/span> <span>len<\/span> = user.name?.length;<\/code><\/pre>\n<p>Optional Chaining\u304c\u6d3b\u304d\u308b\u30dd\u30a4\u30f3\u30c8\u3067\u3059\u3002<br \/>\u305f\u3060\u3057\u3001Optional Chaining\u306b\u3082\u6ce8\u610f\u70b9\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n<ul>\n<li>\n<p>\u5b58\u5728\u3057\u306a\u3044\u30d7\u30ed\u30d1\u30c6\u30a3\u3092\u53c2\u7167\u3057\u3066\u3082\u30a8\u30e9\u30fc\u304c\u51fa\u306a\u3044\u305f\u3081\u3001\u4e0d\u5177\u5408\u306e\u767a\u898b\u304c\u9045\u308c\u308b\u53ef\u80fd\u6027\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n<\/li>\n<li>\n<p>\u9023\u9396\u7684\u306b\u4f7f\u7528\u3057\u3059\u304e\u308b\u3068\u3001\u30b3\u30fc\u30c9\u306e\u610f\u56f3\u304c\u4e0d\u660e\u77ad\u306b\u306a\u308b\u3053\u3068\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n<\/li>\n<li>\n<p>\u66d6\u6627\u306a\u8a2d\u8a08\u306e\u307e\u307e\u3067\u3082\u30b3\u30fc\u30c9\u304c\u901a\u3063\u3066\u3057\u307e\u3046\u305f\u3081\u3001\u9069\u5207\u306a\u30d0\u30ea\u30c7\u30fc\u30b7\u30e7\u30f3\u3092\u7701\u7565\u3057\u304c\u3061\u3067\u3059\u3002<\/p>\n<\/li>\n<\/ul>\n<p>\u3042\u304f\u307e\u3067\u300c\u5b89\u5168\u306b\u30a2\u30af\u30bb\u30b9\u3059\u308b\u88dc\u52a9\u7684\u306a\u624b\u6bb5\u300d\u3068\u3057\u3066\u4f7f\u3044\u3001\u5fc5\u8981\u306a\u30d0\u30ea\u30c7\u30fc\u30b7\u30e7\u30f3\u3084\u30c1\u30a7\u30c3\u30af\u51e6\u7406\u3068\u4f75\u7528\u3059\u308b\u306e\u304c\u30d9\u30b9\u30c8\u3067\u3059\u3002<\/p>\n<h3>\u843d\u3068\u3057\u7a742\uff1athis\u306e\u8aa4\u89e3<\/h3>\n<pre><code><span>const<\/span> obj = {\r\n  <span>value<\/span>: <span>42<\/span>,\r\n  <span>logValue<\/span>: <span><span>function<\/span>(<span><\/span>) <\/span>{\r\n    setTimeout(<span><span>function<\/span>(<span><\/span>) <\/span>{\r\n      <span>console<\/span>.log(<span>this<\/span>.value); <span>\/\/ undefined<\/span>\r\n    }, <span>1000<\/span>);\r\n  }\r\n};<\/code><\/pre>\n<p>\u3053\u306e\u5834\u5408\u3001\u666e\u901a\u306efunction\u306f\u5225\u30b9\u30b3\u30fc\u30d7\u306ethis\u306b\u306a\u308b\u305f\u3081\u6ce8\u610f\u304c\u5fc5\u8981\u3067\u3059\u3002<\/p>\n<p>\u2192 \u30a2\u30ed\u30fc\u95a2\u6570\u3067\u56de\u907f\u53ef\u80fd\uff01<\/p>\n<h3>\u843d\u3068\u3057\u7a743\uff1aforEach\u3067\u975e\u540c\u671f\u51e6\u7406\u3057\u306a\u3044<\/h3>\n<pre><code><span>\/\/ NG<\/span>\r\nitems.forEach(<span>async<\/span> item =&gt; {\r\n  <span>await<\/span> doSomething(item); <span>\/\/ \u52d5\u304b\u306a\u3044<\/span>\r\n});\r\n\r\n<span>\/\/ OK<\/span>\r\n<span>for<\/span> (<span>const<\/span> item <span>of<\/span> items) {\r\n  <span>await<\/span> doSomething(item);\r\n}<\/code><\/pre>\n<p>forEach\u306f\u975e\u540c\u671f\u306e\u51e6\u7406\u306b\u5411\u3044\u3066\u3044\u307e\u305b\u3093\u3002\u7d20\u76f4\u306bfor&#8230;of\u3092\u4f7f\u3044\u307e\u3057\u3087\u3046\u3002<\/p>\n<hr>\n<h2>\u6b21\u306b\u5b66\u3076\u3079\u304d\u30b9\u30c6\u30c3\u30d7\u3068\u5b9f\u52d9\u3078\u306e\u5fdc\u7528<\/h2>\n<p>\u4eca\u56de\u7d39\u4ecb\u3057\u305f\u30c6\u30af\u30cb\u30c3\u30af\u306f\u3001\u3059\u3079\u3066\u73fe\u5834\u3067\u5f79\u7acb\u3064\u3082\u306e\u3070\u304b\u308a\u3067\u3059\u3002\u7279\u306b\u30c1\u30fc\u30e0\u958b\u767a\u3067\u306f\u300c\u8aad\u307f\u3084\u3059\u3055\u300d\u300c\u4fdd\u5b88\u6027\u300d\u304c\u5927\u5207\u3067\u3059\u3002<\/p>\n<hr>\n<h3>\u3010\u5916\u90e8\u30ea\u30f3\u30af\u3011<\/h3>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/JavaScript\/Reference\/Operators\/Destructuring_assignment\">MDN Web Docs: Destructuring assignment<\/a><\/p>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/JavaScript\/Reference\/Operators\/Nullish_coalescing_operator\">MDN Web Docs: Nullish coalescing operator (??)<\/a><\/p>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/JavaScript\/Reference\/Operators\/Optional_chaining\">MDN Web Docs: Optional chaining (?.)<\/a><\/p>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/JavaScript\/Reference\/Functions\/Arrow_functions\">MDN Web Docs: Arrow functions<\/a><\/p>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/JavaScript\/Reference\/Operators\/Spread_syntax\">MDN Web Docs: Spread syntax<\/a><\/p>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/JavaScript\/Reference\/Template_literals\">MDN Web Docs: Template literals<\/a><\/p>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/JavaScript\/Reference\/Global_Objects\/Array\/map\">MDN Web Docs: Array.prototype.map()<\/a><\/p>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/JavaScript\/Reference\/Statements\/async_function\">MDN Web Docs: async function<\/a><\/p>\n<h3>\u3010\u5185\u90e8\u30ea\u30f3\u30af\u3011<\/h3>\n<p><a href=\"https:\/\/route-zero.com\/recruit\/route\/1109\/\">JavaScript\u3067\u3088\u304f\u767a\u751f\u3059\u308b\u30a8\u30e9\u30fc\u300cReferenceError\u300d\u300cSyntaxError\u300d\u306a\u3069\u306e\u539f\u56e0\u3068\u5bfe\u7b56\u3092\u5177\u4f53\u4f8b\u4ed8\u304d\u3067\u89e3\u8aac<\/a><\/p>\n<p><a href=\"https:\/\/route-zero.com\/recruit\/route\/917\/\">JavaScript\u306e\u30b3\u30fc\u30eb\u30d0\u30c3\u30af\u304c\u308f\u304b\u3089\u306a\u3044\uff1f\u30a2\u30cb\u30e1\u30fc\u30b7\u30e7\u30f3\u5b9f\u4f8b\u3067\u3084\u3055\u3057\u304f\u89e3\u8aac\uff01<\/a><\/p>\n<p><a href=\"https:\/\/route-zero.com\/recruit\/route\/965\/\">JavaScript\u306e\u914d\u5217\u30fbJSON\u30fbmap\u30fbMap\uff1a\u30c7\u30fc\u30bf\u64cd\u4f5c\u8853<\/a><\/p>\n<\/div>\n","protected":false},"featured_media":1137,"template":"","_links":{"self":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/route\/1136"}],"collection":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/route"}],"about":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/types\/route"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/media\/1137"}],"wp:attachment":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/media?parent=1136"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}