{"id":1229,"date":"2025-05-02T18:41:33","date_gmt":"2025-05-02T09:41:33","guid":{"rendered":"https:\/\/route-zero.com\/recruit\/route\/1229\/"},"modified":"2025-05-22T18:47:55","modified_gmt":"2025-05-22T09:47:55","slug":"1229","status":"publish","type":"route","link":"https:\/\/route-zero.com\/recruit\/route\/1229\/","title":{"rendered":"\u3010\u4fdd\u5b58\u7248\u3011React\u306euseState\u3068useEffect\u306e\u9055\u3044\u3068\u306f\uff1f\u521d\u5fc3\u8005\u304c\u5b9f\u52d9\u3067\u8ff7\u308f\u306a\u3044\u4f7f\u3044\u5206\u3051\u5b8c\u5168\u30ac\u30a4\u30c9"},"content":{"rendered":"<div>\n<h2>useState\u3068useEffect\u3001\u9055\u3044\u3092\u7406\u89e3\u3057\u3066\u3044\u307e\u3059\u304b\uff1f<\/h2>\n<p>React\u958b\u767a\u306b\u304a\u3044\u3066\u3001\u5fc5\u305a\u767b\u5834\u3059\u308b\u306e\u304c useState \u3068 useEffect\u3002\u516c\u5f0f\u30c9\u30ad\u30e5\u30e1\u30f3\u30c8\u3067\u3082\u6700\u521d\u306b\u7d39\u4ecb\u3055\u308c\u3001\u591a\u304f\u306e\u30c1\u30e5\u30fc\u30c8\u30ea\u30a2\u30eb\u306b\u767b\u5834\u3057\u307e\u3059\u3002<\/p>\n<p>\u3067\u3059\u304c\u3001\u3053\u3093\u306a\u7591\u554f\u3092\u6301\u3063\u305f\u3053\u3068\u306f\u3042\u308a\u307e\u305b\u3093\u304b\uff1f<\/p>\n<ul>\n<li>\n<p>useEffect\u3063\u3066\u7d50\u5c40\u3044\u3064\u52d5\u304f\u306e\uff1f<\/p>\n<\/li>\n<li>\n<p>useState\u306e\u66f4\u65b0\u3063\u3066\u540c\u671f\uff1f\u975e\u540c\u671f\uff1f<\/p>\n<\/li>\n<li>\n<p>useEffect\u306e\u4e2d\u3067setState\u3057\u3066\u3044\u3044\u306e\uff1f<\/p>\n<\/li>\n<li>\n<p>\u305d\u3082\u305d\u3082\u3001\u4f55\u3092\u57fa\u6e96\u306b\u4f7f\u3044\u5206\u3051\u308c\u3070\u3044\u3044\u306e\uff1f<\/p>\n<\/li>\n<\/ul>\n<p>\u3053\u308c\u3089\u306fReact\u306b\u304a\u3051\u308b\u300c\u72b6\u614b\u7ba1\u7406\u300d\u3068\u300c\u526f\u4f5c\u7528\u300d\u306e\u9055\u3044\u3092\u6b63\u3057\u304f\u7406\u89e3\u3059\u308b\u3053\u3068\u3067\u3001\u30b9\u30c3\u30ad\u30ea\u89e3\u6d88\u3067\u304d\u307e\u3059\u3002<\/p>\n<p>\u672c\u8a18\u4e8b\u3067\u306f\u3001useState\u3068useEffect\u306e\u9055\u3044\u3068\u5b9f\u52d9\u3067\u306e\u4f7f\u3044\u5206\u3051\u3092\u3001\u521d\u5b66\u8005\u301c\u4e2d\u7d1a\u8005\u5411\u3051\u306b\u4e01\u5be7\u306b\u89e3\u8aac\u3057\u307e\u3059\u3002<\/p>\n<hr>\n<h2>useState\u306e\u5f79\u5272\u3068\u57fa\u672c\u7684\u306a\u4f7f\u3044\u65b9\u3068\u306f\uff1f<\/h2>\n<h3>useState\u3068\u306f\uff1f<\/h3>\n<p>React\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u5185\u3067\u300c\u72b6\u614b\uff08state\uff09\u300d\u3092\u6301\u3064\u305f\u3081\u306eHook\u3067\u3059\u3002\u72b6\u614b\u304c\u5909\u308f\u308b\u3068\u81ea\u52d5\u7684\u306b\u518d\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0\u304c\u767a\u751f\u3057\u307e\u3059\u3002<\/p>\n<pre><code><span>import<\/span> { useState } <span>from<\/span> <span>'react'<\/span>;\r\n\r\n<span>const<\/span> Counter = <span><span>()<\/span> =&gt;<\/span> {\r\n  <span>const<\/span> [count, setCount] = useState(<span>0<\/span>);\r\n\r\n  <span>return<\/span> (\r\n    &lt;div&gt;\r\n      &lt;p&gt;\u30ab\u30a6\u30f3\u30c8: {count}&lt;\/p&gt;\r\n      &lt;button onClick={() =&gt; setCount(count + 1)}&gt;\u5897\u3084\u3059&lt;\/button&gt;\r\n    &lt;\/div&gt;\r\n  );\r\n};<\/code><\/pre>\n<h3>\u3088\u304f\u4f7f\u3046\u5834\u9762<\/h3>\n<ul>\n<li>\n<p>\u30d5\u30a9\u30fc\u30e0\u306e\u5165\u529b\u5024\u3092\u4fdd\u6301<\/p>\n<\/li>\n<li>\n<p>\u30e2\u30fc\u30c0\u30eb\u306e\u8868\u793a\/\u975e\u8868\u793a\u5236\u5fa1<\/p>\n<\/li>\n<li>\n<p>\u30d5\u30a3\u30eb\u30bf\u30fc\u6761\u4ef6\u3084\u30bf\u30d6\u306e\u9078\u629e\u72b6\u614b\u306e\u7ba1\u7406<\/p>\n<\/li>\n<\/ul>\n<hr>\n<h2>useEffect\u306e\u5f79\u5272\u3068\u57fa\u672c\u7684\u306a\u4f7f\u3044\u65b9\u3068\u306f\uff1f<\/h2>\n<h3>useEffect\u3068\u306f\uff1f<\/h3>\n<p>React\u306e\u300c\u526f\u4f5c\u7528\u300d\u3092\u7ba1\u7406\u3059\u308bHook\u3067\u3059\u3002\u526f\u4f5c\u7528\u3068\u306f\u3001<strong>React\u306e\u5916\uff08DOM, API, \u30bf\u30a4\u30de\u30fc\u306a\u3069\uff09\u3068\u306e\u3084\u308a\u53d6\u308a<\/strong>\u3092\u6307\u3057\u307e\u3059\u3002<\/p>\n<pre><code><span>import<\/span> { useEffect, useState } <span>from<\/span> <span>'react'<\/span>;\r\n\r\n<span>const<\/span> Timer = <span><span>()<\/span> =&gt;<\/span> {\r\n  <span>const<\/span> [time, setTime] = useState(<span>0<\/span>);\r\n\r\n  useEffect(<span><span>()<\/span> =&gt;<\/span> {\r\n    <span>const<\/span> id = setInterval(<span><span>()<\/span> =&gt;<\/span> setTime(<span>(<span>t<\/span>) =&gt;<\/span> t + <span>1<\/span>), <span>1000<\/span>);\r\n    <span>return<\/span> <span><span>()<\/span> =&gt;<\/span> clearInterval(id); <span>\/\/ \u30af\u30ea\u30fc\u30f3\u30a2\u30c3\u30d7<\/span>\r\n  }, []);\r\n\r\n  <span>return<\/span> &lt;p&gt;\u7d4c\u904e\u6642\u9593: {time}s&lt;\/p&gt;;\r\n};<\/code><\/pre>\n<h3>\u3088\u304f\u4f7f\u3046\u5834\u9762<\/h3>\n<ul>\n<li>\n<p>\u521d\u56de\u30de\u30a6\u30f3\u30c8\u6642\u306bAPI\u304b\u3089\u30c7\u30fc\u30bf\u53d6\u5f97<\/p>\n<\/li>\n<li>\n<p>\u30bf\u30a4\u30de\u30fc\u3084\u30a4\u30d9\u30f3\u30c8\u30ea\u30b9\u30ca\u30fc\u306e\u767b\u9332\u30fb\u89e3\u9664<\/p>\n<\/li>\n<li>\n<p>\u72b6\u614b\u5909\u5316\u306b\u5fdc\u3058\u305f\u5916\u90e8\u51e6\u7406\uff08\u30d5\u30a7\u30c3\u30c1\u3001DOM\u64cd\u4f5c\uff09<\/p>\n<\/li>\n<\/ul>\n<hr>\n<h2>\u72b6\u614b\u7ba1\u7406\u3068\u526f\u4f5c\u7528\u306e\u95a2\u4fc2\uff08\u56f3\u89e3\uff09<\/h2>\n<pre><code>\u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2510\r\n\u2502 useState   \u2502 \u2190 UI\u306e\u72b6\u614b\uff08\u4f8b: \u5165\u529b\u5024\u3001\u30ab\u30a6\u30f3\u30c8\uff09\r\n\u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518\r\n       \u2502 \u72b6\u614b\u304c\u5909\u308f\u308b\u3068\r\n       \u25bc\r\n\u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2510\r\n\u2502 useEffect  \u2502 \u2190 \u72b6\u614b\u306b\u57fa\u3065\u3044\u3066\u526f\u4f5c\u7528\u3092\u5b9f\u884c\uff08\u4f8b: \u518d\u30d5\u30a7\u30c3\u30c1\uff09\r\n\u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518<\/code><\/pre>\n<p>useState\u3067\u72b6\u614b\u3092\u66f4\u65b0\u3059\u308b\u3068\u3001\u305d\u308c\u3092\u30c8\u30ea\u30ac\u30fc\u306buseEffect\u304c\u8d70\u308b\u3002<br \/><strong>\u3053\u306e\u9023\u52d5\u95a2\u4fc2\u3092\u7406\u89e3\u3059\u308b\u3053\u3068\u304c\u3001React\u306e\u6319\u52d5\u3092\u6b63\u3057\u304f\u5236\u5fa1\u3059\u308b\u7b2c\u4e00\u6b69\u3067\u3059\u3002<\/strong><\/p>\n<hr>\n<h2>\u3088\u304f\u3042\u308b\u3064\u307e\u305a\u304d\u30dd\u30a4\u30f3\u30c8\u3068\u305d\u306e\u56de\u907f\u6cd5<\/h2>\n<h3>useEffect\u306e\u4f9d\u5b58\u914d\u5217\uff08deps\uff09\u30df\u30b9<\/h3>\n<pre><code>useEffect(<span><span>()<\/span> =&gt;<\/span> {\r\n  fetchUser(userId);\r\n}, [userId]); <span>\/\/ &#x2705; userId\u5909\u66f4\u6642\u306b\u518d\u5b9f\u884c<\/span><\/code><\/pre>\n<ul>\n<li>\n<p>[]\uff08\u7a7a\uff09\u306b\u3059\u308b\u3068\u521d\u56de\u306e\u307f<\/p>\n<\/li>\n<li>\n<p>\u66f8\u304d\u5fd8\u308c\u308b\u3068\u6bce\u56de\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0\u3067\u526f\u4f5c\u7528\u304c\u5b9f\u884c<\/p>\n<\/li>\n<li>\n<p>\u95a2\u6570\u3092\u4f9d\u5b58\u306b\u542b\u3081\u308b\u5834\u5408\u3001useCallback\u3084useMemo\u3067\u5b89\u5b9a\u5316\u3057\u306a\u3044\u3068\u7121\u9650\u30eb\u30fc\u30d7\u306e\u539f\u56e0\u306b<\/p>\n<\/li>\n<\/ul>\n<hr>\n<h3>useState\u306e\u66f4\u65b0\u306f\u975e\u540c\u671f\uff01<\/h3>\n<pre><code>setCount(count + <span>1<\/span>);\r\nsetCount(count + <span>1<\/span>); <span>\/\/ &#x274c; \u2192 \u5b9f\u969b\u306f+1\u306e\u307f<\/span>\r\n\r\n<span>\/\/ &#x2705; \u6b63\u3057\u3044\u65b9\u6cd5<\/span>\r\nsetCount(<span>(<span>prev<\/span>) =&gt;<\/span> prev + <span>1<\/span>);\r\nsetCount(<span>(<span>prev<\/span>) =&gt;<\/span> prev + <span>1<\/span>); <span>\/\/ \u2192 \u6b63\u3057\u304f+2\u306b\u306a\u308b<\/span><\/code><\/pre>\n<p><strong>\u72b6\u614b\u66f4\u65b0\u306f\u300c\u30d0\u30c3\u30c1\u51e6\u7406\u300d\u3055\u308c\u308b<\/strong>\u305f\u3081\u3001\u540c\u3058\u5024\u306b\u4f9d\u5b58\u3059\u308bsetState\u3092\u9023\u7d9a\u3057\u3066\u4f7f\u3046\u3068\u610f\u56f3\u901a\u308a\u52d5\u304d\u307e\u305b\u3093\u3002<\/p>\n<hr>\n<h3>\u3042\u308a\u304c\u3061\u306a\u5931\u6557\u4f8b\u3068\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9\uff08API\u7de8\uff09<\/h3>\n<p>\u5931\u6557\u30d1\u30bf\u30fc\u30f3\uff08\u6bce\u56de\u30d5\u30a7\u30c3\u30c1\uff09<\/p>\n<pre><code><span>const<\/span> [user, setUser] = useState(<span>null<\/span>);\r\n<span>const<\/span> data = fetch(<span>'\/api\/user'<\/span>); <span>\/\/ &#x274c;\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0\u3054\u3068\u306b\u547c\u3070\u308c\u308b<\/span>\r\n\r\nsetUser(data);<\/code><\/pre>\n<p>\u6b63\u3057\u3044\u66f8\u304d\u65b9<\/p>\n<pre><code>useEffect(<span><span>()<\/span> =&gt;<\/span> {\r\n  fetch(<span>'\/api\/user'<\/span>)\r\n    .then(<span><span>res<\/span> =&gt;<\/span> res.json())\r\n    .then(<span><span>data<\/span> =&gt;<\/span> setUser(data));\r\n}, []); <span>\/\/ &#x2705; \u521d\u56de\u3060\u3051\u5b9f\u884c<\/span><\/code><\/pre>\n<p><strong>\u30dd\u30a4\u30f3\u30c8\uff1aAPI\u901a\u4fe1\u306fuseEffect\u3067\u5236\u5fa1\u3057\u3001\u53d6\u5f97\u30c7\u30fc\u30bf\u306fuseState\u306b\u4fdd\u6301\u3002\u3053\u308c\u304cReact\u306e\u57fa\u672c\u5f62\u3067\u3059\u3002<\/strong><\/p>\n<hr>\n<h2>useState\u3068useEffect\u306e\u4f7f\u3044\u5206\u3051\u65b9\u307e\u3068\u3081<\/h2>\n<h3>useState\u304c\u9069\u3057\u3066\u3044\u308b\u5834\u9762<\/h3>\n<ul>\n<li>\n<p>\u5165\u529b\u5024\u3001\u30c1\u30a7\u30c3\u30af\u72b6\u614b\u306a\u3069UI\u4e0a\u306e<strong>\u53ef\u5909\u30c7\u30fc\u30bf<\/strong><\/p>\n<\/li>\n<li>\n<p>\u72b6\u614b\u5909\u5316\u304c\u753b\u9762\u306b\u5373\u6642\u53cd\u6620\u3055\u308c\u308b\u3082\u306e<\/p>\n<\/li>\n<\/ul>\n<h3>useEffect\u304c\u5fc5\u8981\u306a\u5834\u9762<\/h3>\n<ul>\n<li>\n<p>\u5916\u90e8\u3068\u306e\u901a\u4fe1\u3084\u526f\u4f5c\u7528\u3092\u767a\u751f\u3055\u305b\u308b\u51e6\u7406<\/p>\n<\/li>\n<li>\n<p>DOM\u64cd\u4f5c\u3084\u30bf\u30a4\u30de\u30fc\u3001\u30a4\u30d9\u30f3\u30c8\u30ea\u30b9\u30ca\u30fc\u306a\u3069<\/p>\n<\/li>\n<\/ul>\n<hr>\n<h2>\u3010\u8a2d\u8a08\u306e\u6307\u91dd\u3011\u8ff7\u3063\u305f\u3068\u304d\u306e\u5224\u65ad\u30c1\u30e3\u30fc\u30c8<\/h2>\n<p><strong>\u3053\u306e\u51e6\u7406\u3001UI\u306e\u5185\u90e8\u3060\u3051\u3067\u5b8c\u7d50\u3059\u308b\uff1f<\/strong><\/p>\n<ul>\n<li>\n<p>\u2192 Yes \u2192 useState<\/p>\n<\/li>\n<li>\n<p>\u2192 No\uff08API\u901a\u4fe1\u30fb\u30bf\u30a4\u30de\u30fc\u30fbDOM\u64cd\u4f5c\u306a\u3069\u542b\u3080\uff09\u2192 useEffect<\/p>\n<\/li>\n<\/ul>\n<hr>\n<h2>\u307e\u3068\u3081\uff5cHooks\u306f\u300c\u72b6\u614b\u300d\u304b\u300c\u526f\u4f5c\u7528\u300d\u304b\u3067\u4f7f\u3044\u5206\u3051\u3088\u3046<\/h2>\n<p>React\u3067\u306f\u3001<strong>\u300c\u72b6\u614b\uff08useState\uff09\u300d\u3068\u300c\u526f\u4f5c\u7528\uff08useEffect\uff09\u300d\u306e\u533a\u5225\u304c\u975e\u5e38\u306b\u91cd\u8981<\/strong>\u3067\u3059\u3002<\/p>\n<p>\u4f7f\u3044\u65b9\u3092\u306a\u3093\u3068\u306a\u304f\u7406\u89e3\u3057\u3066\u3044\u308b\u3060\u3051\u3067\u306f\u3001\u610f\u56f3\u3057\u306a\u3044\u518d\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0\u3084\u7121\u9650\u30eb\u30fc\u30d7\u306e\u539f\u56e0\u306b\u306a\u308a\u307e\u3059\u3002<\/p>\n<p>\u8ff7\u3063\u305f\u3068\u304d\u306f\u3001\u305c\u3072\u3053\u306e\u8a18\u4e8b\u3067\u7d39\u4ecb\u3057\u305f\u539f\u5247\u306b\u7acb\u3061\u8fd4\u3063\u3066\u307f\u3066\u304f\u3060\u3055\u3044\u3002<\/p>\n<h3>\u3010\u5916\u90e8\u30ea\u30f3\u30af\u3011<\/h3>\n<p><a href=\"https:\/\/ja.react.dev\/learn\/state-a-components-memory\">React\u516c\u5f0f: useState\u306e\u89e3\u8aac<\/a><\/p>\n<p><a href=\"https:\/\/ja.react.dev\/learn\/synchronizing-with-effects\">React\u516c\u5f0f: useEffect\u306e\u89e3\u8aac<\/a><\/p>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/JavaScript\/Reference\/Global_Objects\/Promise\">MDN: Promise<\/a><\/p>\n<p><a href=\"https:\/\/developer.mozilla.org\/ja\/docs\/Web\/API\/Fetch_API\">MDN: Fetch API<\/a><\/p>\n<h3>\u3010\u5185\u90e8\u30ea\u30f3\u30af\u3011<\/h3>\n<p><a href=\"https:\/\/route-zero.com\/recruit\/route\/1219\/\">\u3010\u5b8c\u5168\u7248\u3011\u578b\u306e\u5909\u63db\u3068\u306f\uff1f\u30ad\u30e3\u30b9\u30c8\u306e\u57fa\u672c\u3068\u843d\u3068\u3057\u7a74\u300d | Java\u30fbJavaScript\u30fbTypeScript\u3067\u5fb9\u5e95\u7406\u89e3\u3059\u308b\u578b\u306e\u6271\u3044\u65b9<\/a><\/p>\n<p><a href=\"https:\/\/route-zero.com\/recruit\/route\/1212\/\">\u975e\u540c\u671f\u51e6\u7406\u306e\u57fa\u672c\u3092\u7406\u89e3\uff5csetTimeout\u30fbPromise\u30fbasync\/await\u306e\u9055\u3044\u3068\u4f7f\u3044\u65b9<\/a><\/p>\n<\/p>\n<\/div>\n","protected":false},"featured_media":1230,"template":"","_links":{"self":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/route\/1229"}],"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\/1230"}],"wp:attachment":[{"href":"https:\/\/route-zero.com\/recruit\/wp-json\/wp\/v2\/media?parent=1229"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}