{"id":3418,"date":"2026-09-24T08:38:07","date_gmt":"2026-09-23T23:38:07","guid":{"rendered":"https:\/\/qol-kk.com\/wp2\/?p=3418"},"modified":"2026-09-24T08:38:07","modified_gmt":"2026-09-23T23:38:07","slug":"20260916-plan031","status":"publish","type":"post","link":"https:\/\/qol-kk.com\/wp2\/blog\/2026\/09\/24\/20260916-plan031\/","title":{"rendered":"React \u306e useEffect \u5b8c\u5168\u7406\u89e3 \u2014 \u4f9d\u5b58\u914d\u5217\u306e\u7f60"},"content":{"rendered":"<h2>\u6982\u8981<\/h2>\n<p><code>useEffect<\/code> \u306f React \u306e\u30d5\u30c3\u30af\u306e\u4e2d\u3067\u3082\u6700\u3082\u4f7f\u3046\u6a5f\u4f1a\u304c\u591a\u304f\u3001\u305d\u3057\u3066\u6700\u3082\u8aa4\u89e3\u3055\u308c\u3084\u3059\u3044\u3082\u306e\u3067\u3059\u3002\u7279\u306b\u300c\u4f9d\u5b58\u914d\u5217\uff08\u7b2c2\u5f15\u6570\uff09\u306b\u4f55\u3092\u66f8\u304f\u304b\u300d\u3067\u6319\u52d5\u304c\u5927\u304d\u304f\u5909\u308f\u308a\u3001\u521d\u5fc3\u8005\u304c\u30cf\u30de\u308b\u539f\u56e0\u306e\u5927\u534a\u306f\u3053\u3053\u306b\u96c6\u4e2d\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n<p>\u3053\u306e\u8a18\u4e8b\u3067\u306f\u3001<code>useEffect<\/code> \u306e\u57fa\u672c\u7684\u306a\u8003\u3048\u65b9\u304b\u3089\u3001\u4f9d\u5b58\u914d\u5217\u306b\u307e\u3064\u308f\u308b\u4ee3\u8868\u7684\u306a\u7f60\u3001\u305d\u3057\u3066\u305d\u306e\u56de\u907f\u65b9\u6cd5\u307e\u3067\u3092\u3001\u52d5\u304f\u6700\u5c0f\u30b3\u30fc\u30c9\u3068\u3068\u3082\u306b\u6574\u7406\u3057\u307e\u3059\u3002<\/p>\n<h2>useEffect \u306e\u57fa\u672c\u30e2\u30c7\u30eb<\/h2>\n<p><code>useEffect<\/code> \u306f\u300c\u30ec\u30f3\u30c0\u30fc\u5f8c\u306b\u5b9f\u884c\u3055\u308c\u308b\u526f\u4f5c\u7528\u300d\u3092\u5ba3\u8a00\u3059\u308b\u305f\u3081\u306e\u3082\u306e\u3067\u3059\u3002\u30dd\u30a4\u30f3\u30c8\u306f\u300c\u3044\u3064\u5b9f\u884c\u3055\u308c\u308b\u304b\u306f\u4f9d\u5b58\u914d\u5217\u304c\u6c7a\u3081\u308b\u300d\u3053\u3068\u3067\u3059\u3002<\/p>\n<pre class=\"lang:default decode:true\">useEffect(() =&gt; {\n  \/\/ \u526f\u4f5c\u7528\uff08\u30c7\u30fc\u30bf\u53d6\u5f97\u30fb\u8cfc\u8aad\u30fbDOM\u64cd\u4f5c\u306a\u3069\uff09\n  return () =&gt; {\n    \/\/ \u30af\u30ea\u30fc\u30f3\u30a2\u30c3\u30d7\uff08\u8cfc\u8aad\u89e3\u9664\u306a\u3069\uff09\n  };\n}, [dep1, dep2]); \/\/ \u4f9d\u5b58\u914d\u5217<\/pre>\n<p>\u4f9d\u5b58\u914d\u5217\u306e\u6307\u5b9a\u306b\u3088\u3063\u3066\u6319\u52d5\u306f3\u30d1\u30bf\u30fc\u30f3\u306b\u5206\u304b\u308c\u307e\u3059\u3002<\/p>\n<pre class=\"lang:default decode:true\">\/\/ 1. \u6bce\u30ec\u30f3\u30c0\u30fc\u5f8c\u306b\u5b9f\u884c\nuseEffect(() =&gt; { \/* ... *\/ });\n\n\/\/ 2. \u521d\u56de\u30de\u30a6\u30f3\u30c8\u6642\u306e\u307f\u5b9f\u884c\nuseEffect(() =&gt; { \/* ... *\/ }, []);\n\n\/\/ 3. dep \u304c\u5909\u5316\u3057\u305f\u3068\u304d\u3060\u3051\u5b9f\u884c\nuseEffect(() =&gt; { \/* ... *\/ }, [dep]);<\/pre>\n<p>\u91cd\u8981\u306a\u306e\u306f\u3001React \u304c\u4f9d\u5b58\u914d\u5217\u306e\u5404\u8981\u7d20\u3092\u300c\u524d\u56de\u306e\u30ec\u30f3\u30c0\u30fc\u306e\u5024\u300d\u3068 <code>Object.is<\/code> \u3067\u6bd4\u8f03\u3057\u3066\u3044\u308b\u70b9\u3067\u3059\u3002\u3053\u306e\u4ed5\u7d44\u307f\u3092\u7406\u89e3\u3057\u3066\u3044\u306a\u3044\u3068\u3001\u4ee5\u964d\u306e\u7f60\u306b\u3059\u3079\u3066\u30cf\u30de\u308a\u307e\u3059\u3002<\/p>\n<h2>\u7f601: \u4f9d\u5b58\u914d\u5217\u306b\u5618\u3092\u3064\u304f\uff08\u5024\u3092\u66f8\u304b\u306a\u3044\uff09<\/h2>\n<p>effect \u306e\u4e2d\u3067\u4f7f\u3063\u3066\u3044\u308b\u5024\u3092\u3001\u4f9d\u5b58\u914d\u5217\u306b\u66f8\u304b\u306a\u3044\u30b1\u30fc\u30b9\u3067\u3059\u3002<\/p>\n<pre class=\"lang:default decode:true\">function Counter({ step }) {\n  const [count, setCount] = useState(0);\n\n  useEffect(() =&gt; {\n    const id = setInterval(() =&gt; {\n      setCount((c) =&gt; c + step);\n    }, 1000);\n    return () =&gt; clearInterval(id);\n  }, []); \/\/ \u2190 step \u304c\u629c\u3051\u3066\u3044\u308b\n\n  return &lt;p&gt;{count}&lt;\/p&gt;;\n}<\/pre>\n<p>\u3053\u306e\u30b3\u30fc\u30c9\u306f\u521d\u56de\u30de\u30a6\u30f3\u30c8\u6642\u306e <code>step<\/code> \u3092\u9589\u3058\u8fbc\u3081\u3066\u3057\u307e\u3044\u3001\u3042\u3068\u3067 <code>step<\/code> \u304c\u5909\u308f\u3063\u3066\u3082\u53e4\u3044\u5024\u3092\u53c2\u7167\u3057\u7d9a\u3051\u307e\u3059\u3002\u3053\u308c\u304c <strong>stale closure\uff08\u53e4\u3044\u5024\u306e\u9589\u3058\u8fbc\u3081\uff09<\/strong> \u3067\u3059\u3002<code>exhaustive-deps<\/code> \u30eb\u30fc\u30eb\u306f\u3053\u308c\u3092\u8b66\u544a\u3057\u307e\u3059\u3002\u307e\u305a\u306f\u7d20\u76f4\u306b\u4f9d\u5b58\u3078\u5165\u308c\u307e\u3057\u3087\u3046\u3002<\/p>\n<pre class=\"lang:default decode:true\">}, [step]);<\/pre>\n<h2>\u7f602: \u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u30fb\u914d\u5217\u30fb\u95a2\u6570\u3092\u4f9d\u5b58\u306b\u5165\u308c\u308b<\/h2>\n<p>\u4f9d\u5b58\u914d\u5217\u306f <code>Object.is<\/code> \u6bd4\u8f03\u306e\u305f\u3081\u3001\u6bce\u30ec\u30f3\u30c0\u30fc\u3067\u65b0\u3057\u3044\u53c2\u7167\u304c\u4f5c\u3089\u308c\u308b\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u30fb\u914d\u5217\u30fb\u95a2\u6570\u306f\u6bce\u56de\u300c\u5909\u308f\u3063\u305f\u300d\u3068\u5224\u5b9a\u3055\u308c\u307e\u3059\u3002<\/p>\n<pre class=\"lang:default decode:true\">function Search({ query }) {\n  const options = { query, limit: 20 }; \/\/ \u6bce\u30ec\u30f3\u30c0\u30fc\u65b0\u3057\u3044\u53c2\u7167\n\n  useEffect(() =&gt; {\n    fetchData(options);\n  }, [options]); \/\/ \u6bce\u30ec\u30f3\u30c0\u30fc\u5b9f\u884c\u3055\u308c\u3066\u3057\u307e\u3046\n}<\/pre>\n<h3>\u5bfe\u7b56A: \u30d7\u30ea\u30df\u30c6\u30a3\u30d6\u306b\u5206\u89e3\u3059\u308b<\/h3>\n<pre class=\"lang:default decode:true\">useEffect(() =&gt; {\n  fetchData({ query, limit: 20 });\n}, [query]);<\/pre>\n<h3>\u5bfe\u7b56B: useMemo \/ useCallback \u3067\u53c2\u7167\u3092\u5b89\u5b9a\u3055\u305b\u308b<\/h3>\n<pre class=\"lang:default decode:true\">const options = useMemo(() =&gt; ({ query, limit: 20 }), [query]);\nuseEffect(() =&gt; {\n  fetchData(options);\n}, [options]);<\/pre>\n<pre class=\"lang:default decode:true\">const handleFetch = useCallback(() =&gt; {\n  fetchData(query);\n}, [query]);\nuseEffect(() =&gt; {\n  handleFetch();\n}, [handleFetch]);<\/pre>\n<h2>\u7f603: \u30af\u30ea\u30fc\u30f3\u30a2\u30c3\u30d7\u3092\u5fd8\u308c\u3066\u975e\u540c\u671f\u304c\u7af6\u5408\u3059\u308b<\/h2>\n<p>\u30c7\u30fc\u30bf\u53d6\u5f97\u3067\u30af\u30ea\u30fc\u30f3\u30a2\u30c3\u30d7\u3092\u66f8\u304b\u306a\u3044\u3068\u3001\u53e4\u3044\u30ea\u30af\u30a8\u30b9\u30c8\u304c\u5f8c\u3067\u89e3\u6c7a\u3057\u3066\u65b0\u3057\u3044\u7d50\u679c\u3092\u4e0a\u66f8\u304d\u3059\u308b <strong>\u30ec\u30fc\u30b9\u30b3\u30f3\u30c7\u30a3\u30b7\u30e7\u30f3<\/strong> \u304c\u8d77\u304d\u307e\u3059\u3002<\/p>\n<pre class=\"lang:default decode:true\">useEffect(() =&gt; {\n  let active = true;\n  fetch(`\/api\/users\/${userId}`)\n    .then((res) =&gt; res.json())\n    .then((data) =&gt; {\n      if (active) setUser(data);\n    });\n  return () =&gt; {\n    active = false;\n  };\n}, [userId]);<\/pre>\n<p><code>AbortController<\/code> \u3092\u4f7f\u3048\u3070\u30ea\u30af\u30a8\u30b9\u30c8\u81ea\u4f53\u3092\u30ad\u30e3\u30f3\u30bb\u30eb\u3067\u304d\u307e\u3059\u3002<\/p>\n<pre class=\"lang:default decode:true\">useEffect(() =&gt; {\n  const controller = new AbortController();\n  fetch(`\/api\/users\/${userId}`, { signal: controller.signal })\n    .then((res) =&gt; res.json())\n    .then(setUser)\n    .catch((err) =&gt; {\n      if (err.name !== \"AbortError\") throw err;\n    });\n  return () =&gt; controller.abort();\n}, [userId]);<\/pre>\n<h2>\u7f604: \u95a2\u6570\u66f4\u65b0\u3067\u4f9d\u5b58\u3092\u6e1b\u3089\u3059<\/h2>\n<p>state \u3092\u300c\u524d\u306e\u5024\u304b\u3089\u8a08\u7b97\u3059\u308b\u300d\u5834\u5408\u306f\u3001\u95a2\u6570\u66f4\u65b0\u5f62\u5f0f\u3092\u4f7f\u3046\u3053\u3068\u3067 state \u81ea\u4f53\u3092\u4f9d\u5b58\u304b\u3089\u5916\u305b\u307e\u3059\u3002<\/p>\n<pre class=\"lang:default decode:true\">useEffect(() =&gt; {\n  const id = setInterval(() =&gt; {\n    setCount((c) =&gt; c + 1); \/\/ count \u3092\u4f9d\u5b58\u306b\u5165\u308c\u306a\u304f\u3066\u3088\u3044\n  }, 1000);\n  return () =&gt; clearInterval(id);\n}, []);<\/pre>\n<p><code>setCount(count + 1)<\/code> \u3060\u3068 <code>count<\/code> \u3092\u4f9d\u5b58\u306b\u5165\u308c\u308b\u5fc5\u8981\u304c\u3042\u308a\u307e\u3059\u304c\u3001<code>setCount((c) =&gt; c + 1)<\/code> \u306a\u3089\u4e0d\u8981\u3067\u3059\u3002<\/p>\n<h2>\u78ba\u8a8d\u65b9\u6cd5<\/h2>\n<ul>\n<li>ESLint \u306e <code>react-hooks\/exhaustive-deps<\/code> \u3092\u6709\u52b9\u306b\u3059\u308b\u3068\u3001\u4f9d\u5b58\u6f0f\u308c\u306f\u307b\u307c\u691c\u51fa\u3067\u304d\u307e\u3059\u3002<\/li>\n<li>\u7121\u9650\u30eb\u30fc\u30d7\u3092\u7591\u3046\u3068\u304d\u306f effect \u5185\u306b <code>console.log<\/code> \u3092\u4ed5\u8fbc\u307f\u3001\u5b9f\u884c\u56de\u6570\u3092\u78ba\u8a8d\u3057\u307e\u3059\u3002<\/li>\n<li>React 18 \u306e Strict Mode \u306f\u958b\u767a\u6642\u306b effect \u30922\u56de\u5b9f\u884c\u3057\u307e\u3059\u3002\u3053\u308c\u306f\u30af\u30ea\u30fc\u30f3\u30a2\u30c3\u30d7\u306e\u4e0d\u5099\u3092\u3042\u3076\u308a\u51fa\u3059\u4ed5\u69d8\u3067\u3001\u672c\u756a\u3067\u306f1\u56de\u3067\u3059\u3002<\/li>\n<\/ul>\n<h2>\u6ce8\u610f\u70b9<\/h2>\n<ul>\n<li>\u8b66\u544a\u3092\u6d88\u3059\u305f\u3081\u306b\u4f9d\u5b58\u914d\u5217\u306b\u5618\u3092\u66f8\u304b\u306a\u3044\u3002<\/li>\n<li>\u30ec\u30f3\u30c0\u30fc\u4e2d\u306b\u8a08\u7b97\u3067\u304d\u308b\u6d3e\u751f\u5024\u306f effect \u3067\u306f\u306a\u304f\u901a\u5e38\u306e\u5909\u6570\uff08\u5fc5\u8981\u306a\u3089 <code>useMemo<\/code>\uff09\u3067\u6c42\u3081\u308b\u3002<\/li>\n<li>\u30e6\u30fc\u30b6\u30fc\u64cd\u4f5c\u306e\u51e6\u7406\u306f effect \u3067\u306f\u306a\u304f\u30a4\u30d9\u30f3\u30c8\u30cf\u30f3\u30c9\u30e9\u306b\u66f8\u304f\u3002<\/li>\n<\/ul>\n<h2>\u307e\u3068\u3081<\/h2>\n<p><code>useEffect<\/code> \u306e\u7f60\u306e\u5927\u534a\u306f\u300c\u4f9d\u5b58\u914d\u5217\u306f <code>Object.is<\/code> \u6bd4\u8f03\u3067\u3042\u308b\u300d\u3068\u3044\u3046\u4e00\u70b9\u306b\u96c6\u7d04\u3055\u308c\u307e\u3059\u3002\u4f7f\u3046\u5024\u306f\u7d20\u76f4\u306b\u4f9d\u5b58\u306b\u5165\u308c\u3001\u53c2\u7167\u304c\u5909\u308f\u308b\u3082\u306e\u306f\u5206\u89e3\u304b memo \u5316\u3057\u3001\u975e\u540c\u671f\u306f\u30af\u30ea\u30fc\u30f3\u30a2\u30c3\u30d7\u3067\u7af6\u5408\u3092\u9632\u304e\u3001state \u66f4\u65b0\u306f\u95a2\u6570\u5f62\u5f0f\u3067\u4f9d\u5b58\u3092\u6e1b\u3089\u3059\u3002\u307e\u305a\u306f <code>exhaustive-deps<\/code> \u3092\u6709\u52b9\u306b\u3057\u3001\u8b66\u544a\u306b\u7d20\u76f4\u306b\u5f93\u3046\u3068\u3053\u308d\u304b\u3089\u59cb\u3081\u308b\u306e\u304c\u6700\u77ed\u306e\u7406\u89e3\u30eb\u30fc\u30c8\u3067\u3059\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>useEffect \u306f React \u306e\u30d5\u30c3\u30af\u306e\u4e2d\u3067\u3082\u6700\u3082\u4f7f\u3046\u6a5f\u4f1a\u304c\u591a\u304f\u3001\u305d\u3057\u3066\u6700\u3082\u8aa4\u89e3\u3055\u308c\u3084\u3059\u3044\u3082\u306e\u3067\u3059\u3002\u7279\u306b\u300c\u4f9d\u5b58\u914d\u5217\uff08\u7b2c2\u5f15\u6570\uff09\u306b\u4f55\u3092\u66f8\u304f\u304b\u300d\u3067\u6319\u52d5\u304c\u5927\u304d\u304f\u5909\u308f\u308a\u3001\u521d\u5fc3\u8005\u304c\u30cf\u30de\u308b\u539f\u56e0\u306e\u5927\u534a\u306f\u3053\u3053\u306b\u96c6\u4e2d\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n","protected":false},"author":1,"featured_media":3417,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"sns_share_botton_hide":"","vkExUnit_sns_title":"","_vk_print_noindex":"","sitemap_hide":"","_veu_custom_css":"","veu_display_promotion_alert":"","vkexunit_cta_each_option":"","_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[36],"tags":[1161,890],"class_list":["post-3418","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-javascript-memorandum","tag-react","tag-890"],"veu_head_title_object":{"title":"","add_site_title":""},"jetpack_publicize_connections":[],"jetpack-related-posts":[],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/qol-kk.com\/wp2\/wp-content\/uploads\/2026\/09\/20260916-plan031-thumbnail.jpg","_links":{"self":[{"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/posts\/3418","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/comments?post=3418"}],"version-history":[{"count":1,"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/posts\/3418\/revisions"}],"predecessor-version":[{"id":3439,"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/posts\/3418\/revisions\/3439"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/media\/3417"}],"wp:attachment":[{"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/media?parent=3418"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/categories?post=3418"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/qol-kk.com\/wp2\/wp-json\/wp\/v2\/tags?post=3418"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}