{"id":46771,"date":"2023-11-13T18:20:16","date_gmt":"2023-11-13T09:20:16","guid":{"rendered":"https:\/\/kinsta.com\/jp\/?p=46771&#038;post_type=knowledgebase&#038;preview_id=46771"},"modified":"2025-10-02T04:45:44","modified_gmt":"2025-10-01T19:45:44","slug":"usestate-react","status":"publish","type":"post","link":"https:\/\/kinsta.com\/jp\/blog\/usestate-react\/","title":{"rendered":"React\u3067useState\u30d5\u30c3\u30af\u306e\u5229\u7528\u3092\u958b\u59cb\u3059\u308b"},"content":{"rendered":"<p>React\u306f\u3001\u30e6\u30fc\u30b6\u30fc\u30a4\u30f3\u30bf\u30fc\u30d5\u30a7\u30fc\u30b9\u306e\u69cb\u7bc9\u306b\u4f7f\u7528\u3055\u308c\u308b\u4eba\u6c17\u306e<a href=\"https:\/\/kinsta.com\/jp\/blog\/javascript-libraries\/\">JavaScript\u30e9\u30a4\u30d6\u30e9\u30ea<\/a>\u3067\u3059\u3002\u30d5\u30c3\u30af\u3092\u542b\u3080\u5e45\u5e83\u3044\u6a5f\u80fd\u3067<a href=\"https:\/\/kinsta.com\/jp\/blog\/types-of-developers\/\">\u958b\u767a\u8005<\/a>\u3092\u652f\u63f4\u3057\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u306e\u69cb\u7bc9\u3092\u7c21\u5358\u304b\u3064\u52b9\u7387\u7684\u306a\u3082\u306e\u306b\u3057\u3066\u304f\u308c\u307e\u3059\u3002<\/p>\n<p>\u6700\u3082\u3088\u304f\u4f7f\u308f\u308c\u308b\u30d5\u30c3\u30af\u306e1\u3064\u304c<code>useState<\/code>\u3067\u3059\u3002\u3053\u308c\u3092\u4f7f\u3046\u3053\u3068\u3067\u95a2\u6570\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3067\u624b\u8efd\u306b\u72b6\u614b\uff08state\uff09\u3092\u6271\u3048\u307e\u3059\u3002<\/p>\n<p>\u3053\u306e\u8a18\u4e8b\u3067\u306f\u3001<code>useState<\/code>\u306e\u7528\u9014\u3068\u5b9f\u88c5\u306e\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9\u306b\u3064\u3044\u3066\u8a73\u3057\u304f\u3054\u7d39\u4ecb\u3057\u307e\u3059\u3002<\/p>\n<div><\/div><kinsta-auto-toc heading=\"Table of Contents\" exclude=\"last\" list-style=\"arrow\" selector=\"h2\" count-number=\"-1\"><\/kinsta-auto-toc>\n<h2>useState\u30d5\u30c3\u30af\u3068\u306f<\/h2>\n<p><code>useState<\/code>\u306e\u8a73\u7d30\u306b\u9032\u3080\u524d\u306b\u3001\u307e\u305a\u30d5\u30c3\u30af\u3068\u306f\u4f55\u304b\u3001\u305d\u3057\u3066\u5f93\u6765\u306e\u30af\u30e9\u30b9\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3068\u3069\u3046\u9055\u3046\u306e\u304b\u3092\u7406\u89e3\u3057\u307e\u3057\u3087\u3046\u3002<\/p>\n<p>\u30d5\u30c3\u30af\u3068\u306f\u3001state\u3084\u305d\u306e\u4ed6\u306e<a href=\"https:\/\/kinsta.com\/jp\/blog\/what-is-react-js\/\">React<\/a>\u306e\u6a5f\u80fd\u3092\u95a2\u6570\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3067\u4f7f\u7528\u3067\u304d\u308b\u3088\u3046\u306b\u3059\u308b\u3082\u306e\u3067\u3059\u3002<\/p>\n<p>\u30af\u30e9\u30b9\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3068\u306f\u7570\u306a\u308a\u3001\u95a2\u6570\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u306fstate\uff08\u72b6\u614b\uff09\u3092\u4fdd\u6301\u3059\u308b\u6a5f\u80fd\u3092\u5185\u8535\u3057\u3066\u3044\u307e\u305b\u3093\u3002\u305d\u3053\u3067<code>useState<\/code>\u306e\u3088\u3046\u306a\u30d5\u30c3\u30af\u3092\u4f7f\u3046\u3053\u3068\u3067\u3001\u95a2\u6570\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u306bstate\u3092\u8ffd\u52a0\u3067\u304d\u307e\u3059\u3002<\/p>\n\n<h3>useState\u30d5\u30c3\u30af\u306e\u80cc\u666f<\/h3>\n<p>React 16.8\u3067<code>useState<\/code>\u30d5\u30c3\u30af\u304c\u5c0e\u5165\u3055\u308c\u308b\u4ee5\u524d\u3001\u95a2\u6570\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u305d\u306e\u3082\u306e\u306fstate\u3092\u4fdd\u6301\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u305b\u3093\u3067\u3057\u305f\u3002\u305d\u306e\u4ee3\u308f\u308a\u306b\u3001\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u306estate\u3092\u7ba1\u7406\u3059\u308b\u305f\u3081\u306b\u3001\u30af\u30e9\u30b9\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3084Redux\u306e\u3088\u3046\u306a\u5916\u90e8\u306e\u72b6\u614b\u7ba1\u7406\u30e9\u30a4\u30d6\u30e9\u30ea\u3092\u4f7f\u308f\u306a\u3051\u308c\u3070\u306a\u308a\u307e\u305b\u3093\u3067\u3057\u305f\u3002<\/p>\n<p>\u30af\u30e9\u30b9\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3084\u5916\u90e8\u306e\u72b6\u614b\u7ba1\u7406\u30e9\u30a4\u30d6\u30e9\u30ea\u306f\u4eca\u3067\u3082\u6709\u52b9\u306a\u9078\u629e\u80a2\u3067\u3059\u304c\u3001<code>useState<\/code>\u30d5\u30c3\u30af\u306e\u5c0e\u5165\u306b\u3088\u308a\u3001\u95a2\u6570\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u306bstate\u3092\u8ffd\u52a0\u3059\u308b\u306e\u304c\u975e\u5e38\u306b\u7c21\u5358\u306b\u306a\u308a\u3001React <a href=\"https:\/\/kinsta.com\/jp\/blog\/rest-api-vs-web-api\/\">API<\/a>\u5168\u4f53\u304c\u30b7\u30f3\u30d7\u30eb\u306b\u306a\u3063\u3066\u3044\u307e\u3059\u3002<\/p>\n<p><code>useState<\/code>\u30d5\u30c3\u30af\u306b\u3088\u3063\u3066\u3001\u3042\u3089\u3086\u308b\u30b1\u30fc\u30b9\u3067\u95a2\u6570\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3092\u4f7f\u7528\u3067\u304d\u308b\u3088\u3046\u306b\u306a\u308a\u3001\u5fc5\u8981\u306a\u5b9a\u578b\u30b3\u30fc\u30c9\u306e\u91cf\u304c\u6e1b\u308a\u3001\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u306estate\u3092\u8a55\u4fa1\u3057\u3084\u3059\u304f\u306a\u308a\u307e\u3057\u305f\u3002<\/p>\n<h3>useState\u69cb\u6587\u306e\u69cb\u6210\u8981\u7d20<\/h3>\n<p><code>useState<\/code>\u30d5\u30c3\u30af\u306f\u3001\u5f15\u6570\u3068\u3057\u3066\u521d\u671f\u306estate\u306e\u5024\u3092\u53d6\u308a\u3001\u73fe\u5728\u306estate\u306e\u5024\u3068\uff08\u72b6\u614b\u306e\u5024\u3092\u5909\u66f4\u3059\u308b\u305f\u3081\u306e\uff09\u95a2\u6570\u306e2\u3064\u306e\u8981\u7d20\u3092\u914d\u5217\u3068\u3057\u3066\u8fd4\u3057\u307e\u3059\u3002<\/p>\n<p>\u4ee5\u4e0b\u306e\u69cb\u6587\u3092\u898b\u308b\u3068\u7406\u89e3\u3067\u304d\u308b\u306f\u305a\u3067\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">const [state, setState] = useState(initialState);<\/code><\/pre>\n<ul>\n<li><code>state<\/code>\uff1a\u73fe\u5728\u306estate\u306e\u5024<\/li>\n<li><code>setState<\/code>\uff1astate\u306e\u5024\u3092\u5909\u66f4\u3059\u308b\u306e\u306b\u4f7f\u3046\u95a2\u6570<\/li>\n<li><code>initialState<\/code>\uff1a\u5ba3\u8a00\u3059\u308bstate\u306e\u5909\u6570\u306e\u521d\u671f\u5024\uff08\u4efb\u610f\u3067\u3042\u308a\u5024\u3092\u6307\u5b9a\u3057\u306a\u3044\u3068\u2500\u203b\u63a8\u5968\u3055\u308c\u306a\u3044\u3082\u306e\u306e\u2500\u81ea\u52d5\u3067<code>undefined<\/code>\u306b\u8a2d\u5b9a\u3055\u308c\u308b\uff09<\/li>\n<\/ul>\n<p><code>useState<\/code>\u30d5\u30c3\u30af\u3092\u4f7f\u7528\u3059\u308b\u5834\u5408\u306b\u306f\u3001state\u306e\u5024\u304c\u5909\u66f4\u3055\u308c\u308b\u305f\u3073\u306bReact\u304c\u81ea\u52d5\u3067\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3092\u518d\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0\u3059\u308b\u306e\u3067\u3001\u3053\u306e\u4ed5\u69d8\u306f\u5ff5\u982d\u306b\u7f6e\u304f\u3088\u3046\u306b\u3057\u3066\u304f\u3060\u3055\u3044\u3002<\/p>\n<h2>useState\u30d5\u30c3\u30af\u306e\u4f7f\u3044\u65b9<\/h2>\n<p><code>useState<\/code>\u3092\u5b9f\u88c5\u3059\u308b\u306b\u306f\u3001\u95a2\u6570\u3092\u547c\u3073\u51fa\u3057\u3001\u5f15\u6570\u3068\u3057\u3066\u521d\u671f\u5024\u3092\u6e21\u3057\u307e\u3059\u3002\u95a2\u6570\u306f\u3001\u73fe\u5728\u306estate\u306e\u5024\u3068state\u3092\u66f4\u65b0\u3059\u308b\u95a2\u6570\u3092\u542b\u3080\u914d\u5217\u3092\u8fd4\u3057\u307e\u3059\u3002<\/p>\n<p>\u4ee5\u4e0b\u306f\u3001<code>useState<\/code>\u3092\u4f7f\u3063\u3066\u5358\u7d14\u306a\u30ab\u30a6\u30f3\u30bf\u30fc\u3092\u7ba1\u7406\u3059\u308b\u4f8b\u3067\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">import { useState } from 'react';\n\nfunction Counter() {\n  const [count, setCount] = useState(0);\n\n  return (\n    &lt;div&gt;\n      &lt;p&gt;You clicked {count} times&lt;\/p&gt;\n      &lt;button onClick={() =&gt; setCount(count + 1)}&gt;\n        Click me\n      &lt;\/button&gt;\n    &lt;\/div&gt;\n  );\n}\n\nexport default Counter;<\/code><\/pre>\n<p>\u3053\u306e\u4f8b\u3067\u306f\u3001<code>useState<\/code>\u30d5\u30c3\u30af\u3092\u4f7f\u3063\u3066\u3001<code>count<\/code>\u306e\u72b6\u614b\u30920\u306b\u521d\u671f\u5316\u3057\u307e\u3059\u3002\u6b21\u306b\u3001\u73fe\u5728\u306e\u30ab\u30a6\u30f3\u30c8\u5024\u3068\u30dc\u30bf\u30f3\u3092\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0\u3057\u307e\u3059\u3002\u30dc\u30bf\u30f3\u304c\u30af\u30ea\u30c3\u30af\u3055\u308c\u308b\u3068\uff08<code>setCount<\/code>\u95a2\u6570\u3067\u30a2\u30ed\u30fc\u95a2\u6570\u3092\u8ffd\u52a0\u3057\u305f\u305f\u3081\uff09\u30ab\u30a6\u30f3\u30c8\u306e\u5024\u304c\u5897\u52a0\u3057\u307e\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">&lt;button onClick={() =&gt; setCount(count + 1)}&gt;Click me&lt;\/button&gt;<\/code><\/pre>\n<p><code>useState<\/code>\u30d5\u30c3\u30af\u3092\u4f7f\u7528\u3059\u308b\u969b\u306f\u3001React\u30e9\u30a4\u30d6\u30e9\u30ea\u304b\u3089\u30a4\u30f3\u30dd\u30fc\u30c8\u3059\u308b\u3053\u3068\u3092\u5fd8\u308c\u306a\u3044\u3053\u3068\u304c\u91cd\u8981\u3067\u3059\u3002\u30a4\u30f3\u30dd\u30fc\u30c8\u3092\u5fd8\u308c\u308b\u3068\u3001\u30d5\u30c3\u30af\u3092\u4f7f\u304a\u3046\u3068\u3057\u3066\u3082\u30a8\u30e9\u30fc\u306b\u306a\u308b\u53ef\u80fd\u6027\u304c\u9ad8\u304f\u306a\u308a\u307e\u3059\u3002\u4ee5\u4e0b\u306b\u3001useState\u3092\u30a4\u30f3\u30dd\u30fc\u30c8\u3059\u308b\u65b9\u6cd5\u3092\u793a\u3057\u307e\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">import { useState } from 'react';<\/code><\/pre>\n<p>import\u6587\u306b<code>useState<\/code>\u3092\u542b\u3081\u308b\u3053\u3068\u3067\u3001\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3067<code>useState<\/code>\u30d5\u30c3\u30af\u3092\u4f7f\u3044\u305f\u3044\u3053\u3068\u3092React\u306b\u4f1d\u3048\u3066\u3044\u307e\u3059\u3002<\/p>\n<h2>React\u306euseState\u30d5\u30c3\u30af\u3067\u3042\u3089\u3086\u308b\u30c7\u30fc\u30bf\u578b\u3092\u4f7f\u3046<\/h2>\n<p>React\u306e<code>useState<\/code>\u30d5\u30c3\u30af\u306f\u3001\u6587\u5b57\u5217\u3084\u6570\u5024\u306e\u30c7\u30fc\u30bf\u578b\u3060\u3051\u3092\u7ba1\u7406\u3059\u308b\u3082\u306e\u3067\u306f\u3042\u308a\u307e\u305b\u3093\u3002\u914d\u5217\u3001\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3001\u30d6\u30fc\u30eb\u5024\u306a\u3069\u3001\u3055\u307e\u3056\u307e\u306a\u30c7\u30fc\u30bf\u578b\u306e\u72b6\u614b\u3092\u7ba1\u7406\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n<h3>useState\u30d5\u30c3\u30af\u3067\u914d\u5217\u3092\u4f7f\u3046<\/h3>\n<p><code>useState<\/code>\u30d5\u30c3\u30af\u3092\u4f7f\u3063\u3066\u3001React\u3067\u914d\u5217\u3092\u7ba1\u7406\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u4f8b\u3048\u3070\u3001\u679c\u7269\u306e\u914d\u5217\u304c\u3042\u308c\u3070\u3001\u305d\u306e\u914d\u5217\u3067state\u3092\u521d\u671f\u5316\u53ef\u80fd\u3067\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">import { useState } from 'react';\n\nfunction App() {\n  const [list, setList] = useState(['apple', 'banana', 'orange']);\n\n  const addToList = () =&gt; {\n    const newItem = 'grape';\n    setList([...list, newItem]);\n  };\n\n  return (\n    &lt;div&gt;\n      &lt;ul&gt;\n        {list.map((item) =&gt; (\n          &lt;li key={item}&gt;{item}&lt;\/li&gt;\n        ))}\n      &lt;\/ul&gt;\n      &lt;button onClick={addToList}&gt;\u9805\u76ee\u3092\u8ffd\u52a0&lt;\/button&gt;\n    &lt;\/div&gt;\n  );\n}\n\nexport default App;<\/code><\/pre>\n<p>\u3053\u306e\u4f8b\u3067\u306f\u3001<code>useState<\/code>\u3092\u4f7f\u3063\u3066<code>list<\/code>\u3068\u3044\u3046\u540d\u524d\u306e\u914d\u5217\u3092\u7ba1\u7406\u3057\u3066\u3044\u307e\u3059\u3002 \u521d\u671f\u306e\u72b6\u614b\u306b\u306f\u30013\u3064\u306e\u9805\u76ee\uff08<strong>apple<\/strong>\u3001<strong>banana<\/strong>\u3001<strong>orange<\/strong>\uff09\u3092\u542b\u3080\u914d\u5217\u304c\u8a2d\u5b9a\u3055\u308c\u3066\u3044\u307e\u3059\u3002<\/p>\n<p>\u307e\u305f\u3001<a href=\"https:\/\/kinsta.com\/jp\/blog\/spread-operator-javascript\/\">\u30b9\u30d7\u30ec\u30c3\u30c9\u6f14\u7b97\u5b50<\/a>(<code>...<\/code>) \u3067\u3059\u3079\u3066\u306e\u914d\u5217\u306e\u4e2d\u8eab\u3092\u30b3\u30d4\u30fc\u3057\u3001\u300c\u9805\u76ee\u3092\u8ffd\u52a0\u300d\u30dc\u30bf\u30f3\u304c\u30af\u30ea\u30c3\u30af\u3055\u308c\u308b\u305f\u3073\u306b\u3001<code>list<\/code>\u306e\u914d\u5217\u306b\u65b0\u3057\u304f<strong>grape<\/strong>\u3092\u8ffd\u52a0\u3059\u308b<code>addToList<\/code>\u95a2\u6570\u3082\u4f5c\u6210\u3057\u307e\u3057\u305f\u3002<\/p>\n<p>\u3053\u306e\u64cd\u4f5c\u3092\u30b9\u30bf\u30f3\u30c9\u30a2\u30ed\u30f3\u306e\u95a2\u6570\u3068\u3057\u3066\u4f5c\u6210\u3057\u3001\u300c<strong>Add Item<\/strong>\u300d\u30dc\u30bf\u30f3\u306b\u8ffd\u52a0\u3055\u308c\u305f<code>onClick<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u901a\u3057\u3066\u547c\u3073\u51fa\u3059\u305f\u3081\u306b\u3001\u3053\u3053\u3067\u306f\u3001\u30a2\u30ed\u30fc\u95a2\u6570\u3092\u4f7f\u7528\u3057\u305f\u30a4\u30f3\u30e9\u30a4\u30f3\u3067\u306estate\u66f4\u65b0\u3092\u884c\u3063\u3066\u3044\u307e\u305b\u3093\u3002<\/p>\n<h3>useState\u30d5\u30c3\u30af\u3067\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u4f7f\u7528\u3059\u308b<\/h3>\n<p><code>useState<\/code>\u30d5\u30c3\u30af\u3092\u4f7f\u3063\u3066\u3001React\u3067\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u7ba1\u7406\u3059\u308b\u3053\u3068\u3082\u3067\u304d\u307e\u3059\u3002\u4ee5\u4e0b\u306f\u305d\u306e\u4f8b\u3067\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">import { useState } from 'react';\n\nfunction App() {\n  const [user, setUser] = useState({ name: 'John', age: 30 });\n\n  const handleClick = () =&gt; {\n    setUser({ ...user, age: user.age + 1 });\n  };\n\n  return (\n    &lt;div&gt;\n      &lt;p&gt;Name: {user.name}&lt;\/p&gt;\n      &lt;p&gt;Age: {user.age}&lt;\/p&gt;\n      &lt;button onClick={handleClick}&gt;\u5e74\u9f62\u3092\u5897\u52a0&lt;\/button&gt;\n    &lt;\/div&gt;\n  );\n}\n\nexport default App;<\/code><\/pre>\n<p>\u3053\u306e\u4f8b\u3067\u306f\u3001<code>useState<\/code>\u3092\u4f7f\u3063\u3066user\u3068\u3044\u3046\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u7ba1\u7406\u3057\u3066\u3044\u307e\u3059\u3002<code>user<\/code>\u306e\u521d\u671f\u72b6\u614b\u306f\u3001<strong>name<\/strong>\u3068<strong>age<\/strong>\u306e2\u3064\u306e\u30d7\u30ed\u30d1\u30c6\u30a3\u3092\u542b\u3080\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306b\u8a2d\u5b9a\u3055\u308c\u3066\u3044\u307e\u3059\u3002<\/p>\n<p>\u307e\u305f\u3001\u3059\u3079\u3066\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u30c7\u30fc\u30bf\u3092\u30b9\u30d7\u30ec\u30c3\u30c9\u6f14\u7b97\u5b50 (<code>...<\/code>) \u3067\u30b3\u30d4\u30fc\u3057\u3001\u300c<strong>\u5e74\u9f62\u3092\u5897\u52a0<\/strong>\u300d\u30dc\u30bf\u30f3\u304c\u30af\u30ea\u30c3\u30af\u3055\u308c\u308b\u305f\u3073\u306b\u30e6\u30fc\u30b6\u30fc\u306e\u5e74\u9f62\u3092<strong>1<\/strong>\u5897\u52a0\u3055\u305b\u308b\u95a2\u6570<code>handleClick<\/code>\u3082\u3042\u308a\u307e\u3059\u3002<\/p>\n<p>\u3053\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u5909\u6570\u306b\u4ee3\u5165\u3057\u3001\u305d\u306e\u5909\u6570\u3092\u521d\u671f\u5316\u3067\u304d\u308b\u3068\u3044\u3046\u7279\u5fb4\u3092\u77e5\u3063\u3066\u304a\u304f\u3053\u3068\u304c\u91cd\u8981\u3067\u3059\u3002\u3053\u308c\u306f\u3001\u5927\u304d\u306a\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3084\u914d\u5217\u304c\u3042\u308a\u3001\u7406\u89e3\u3057\u3084\u3059\u3044\u30b3\u30fc\u30c9\u3092\u66f8\u304d\u305f\u3044\u5834\u5408\u306b\u4fbf\u5229\u3067\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">import { useState } from 'react';\n\/\/ Declare data\nlet userData = {\n    name: 'John',\n    age: 30,\n};\n\nfunction App() {\n    const [user, setUser] = useState(userData);\n\n    const handleClick = () =&gt; {\n        setUser({ ...user, age: user.age + 1 });\n    };\n\n    return (\n        &lt;div&gt;\n            &lt;p&gt;Name: {user.name}&lt;\/p&gt;\n            &lt;p&gt;Age: {user.age}&lt;\/p&gt;\n            &lt;button onClick={handleClick}&gt;Increase Age&lt;\/button&gt;\n        &lt;\/div&gt;\n    );\n}\n\nexport default App;<\/code><\/pre>\n<h3>useState\u30d5\u30c3\u30af\u3067\u30d6\u30fc\u30eb\u5024\u3092\u4f7f\u3046<\/h3>\n<p><code>useState<\/code>\u30d5\u30c3\u30af\u3092\u4f7f\u3063\u3066\u3001React\u3067\u30d6\u30fc\u30eb\u5024\u3092\u7ba1\u7406\u3059\u308b\u3053\u3068\u3082\u3067\u304d\u307e\u3059\u3002\u4ee5\u4e0b\u306f\u305d\u306e\u4f8b\u3067\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">import { useState } from 'react';\n\nfunction App() {\n  const [isOn, setIsOn] = useState(false);\n\n  const toggleSwitch = () =&gt; {\n    setIsOn(!isOn);\n  };\n\n  return (\n    &lt;div&gt;\n      &lt;p&gt;The switch is {isOn ? 'on' : 'off'}&lt;\/p&gt;\n      &lt;button onClick={toggleSwitch}&gt;\u30c8\u30b0\u30eb\u30b9\u30a4\u30c3\u30c1&lt;\/button&gt;\n    &lt;\/div&gt;\n  );\n}\n\nexport default App;<\/code><\/pre>\n<p>\u3053\u306e\u4f8b\u3067\u306f\u3001<code>useState<\/code>\u3092\u4f7f\u3063\u3066\u3001<code>isOn<\/code>\u3068\u3044\u3046\u30d6\u30fc\u30eb\u5024\u3092\u7ba1\u7406\u3057\u3066\u3044\u307e\u3059\u3002\u521d\u671f\u306e<code>isOn<\/code>\u306estate\u306f<code>false<\/code>\u306b\u8a2d\u5b9a\u3055\u308c\u3066\u3044\u307e\u3059\u3002\u307e\u305f\u3001\u300c<strong>\u30c8\u30b0\u30eb\u30b9\u30a4\u30c3\u30c1<\/strong>\u300d\u30dc\u30bf\u30f3\u304c\u30af\u30ea\u30c3\u30af\u3055\u308c\u308b\u305f\u3073\u306b<code>isOn<\/code>\u306e\u5024\u3092\u5207\u308a\u66ff\u3048\u308b\u95a2\u6570<code>toggleSwitch<\/code>\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n<p>\u3053\u306e\u6a5f\u80fd\u306f\u3001\u30d7\u30ed\u30b8\u30a7\u30af\u30c8\u3067\u30c0\u30fc\u30af\u30e2\u30fc\u30c9\u3068\u30e9\u30a4\u30c8\u30e2\u30fc\u30c9\u306e\u5207\u308a\u66ff\u3048\u3092\u7ba1\u7406\u3059\u308b\u306e\u306b\u5229\u7528\u3067\u304d\u307e\u3059\u3002<\/p>\n<p>\u6700\u5f8c\u306b\u3001\u30d5\u30a9\u30fc\u30e0\u3092\u4f7f\u3063\u305f<code>useState<\/code>\u30d5\u30c3\u30af\u306e\u9ad8\u5ea6\u306a\u4f7f\u3044\u65b9\u3092\u3054\u7d39\u4ecb\u3057\u307e\u3057\u3087\u3046\u3002<\/p>\n<h2>useState\u30d5\u30c3\u30af\u3068\u30d5\u30a9\u30fc\u30e0<\/h2>\n<p>React\u3067\u30d5\u30a9\u30fc\u30e0\u30c7\u30fc\u30bf\u3068\u30e6\u30fc\u30b6\u30fc\u306b\u3088\u308b\u5165\u529b\u30c7\u30fc\u30bf\u3092\u6271\u3046\u306b\u306f\u3001state\u3092\u4f7f\u3046\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u3053\u308c\u306f\u3001\u30d5\u30a9\u30fc\u30e0\u8981\u7d20\u306e\u73fe\u5728\u306e\u5024\u3092\u8ffd\u8de1\u3059\u308b\u306e\u306b\u4f7f\u308f\u308c\u307e\u3059\u3002\u30c6\u30ad\u30b9\u30c8\u5165\u529b\u3084\u30c9\u30ed\u30c3\u30d7\u30c0\u30a6\u30f3\u304b\u3089\u306e\u30aa\u30d7\u30b7\u30e7\u30f3\u9078\u629e\u306a\u3069\u3001\u3059\u3079\u3066\u306e\u30e6\u30fc\u30b6\u30fc\u30a4\u30f3\u30bf\u30e9\u30af\u30b7\u30e7\u30f3\u3092\u8ffd\u8de1\u3057\u3001\u6700\u5f8c\u306b\u65b0\u3057\u3044\u5024\u3067state\u3092\u66f4\u65b0\u3057\u307e\u3059\u3002<\/p>\n<p>\u3053\u3053\u3067\u306f\u3001<code>useState<\/code>\u3092\u4f7f\u3063\u3066\u30b7\u30f3\u30d7\u30eb\u306a\u30d5\u30a9\u30fc\u30e0\u3092\u4f5c\u6210\u3059\u308b\u4f8b\u3092\u793a\u3057\u307e\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">import { useState } from 'react';\n\nlet formStateData = {\n    firstName: '',\n    lastName: '',\n    email: '',\n};\n\nfunction Form() {\n    const [formData, setFormData] = useState(formStateData);\n\n    const handleInputChange = (event) =&gt; {\n        const { name, value } = event.target;\n        setFormData({ ...formData, [name]: value });\n    };\n\n    const handleSubmit = (event) =&gt; {\n        event.preventDefault();\n        console.log(formData);\n    };\n\n    return (\n        &lt;form onSubmit={handleSubmit}&gt;\n            &lt;input\n                type=\"text\"\n                name=\"firstName\"\n                value={formData.firstName}\n                onChange={handleInputChange}\n            \/&gt;\n            &lt;input\n                type=\"text\"\n                name=\"lastName\"\n                value={formData.lastName}\n                onChange={handleInputChange}\n            \/&gt;\n            &lt;input\n                type=\"email\"\n                name=\"email\"\n                value={formData.email}\n                onChange={handleInputChange}\n            \/&gt;\n            &lt;button type=\"submit\"&gt;Submit&lt;\/button&gt;\n        &lt;\/form&gt;\n    );\n}\n\nexport default Form;<\/code><\/pre>\n<p>\u3053\u306e\u4f8b\u3067\u306f\u3001\u307e\u305a\u3001<strong>firstName<\/strong>\u3001<strong>lastName<\/strong>\u3001<strong>email<\/strong>\u30d5\u30a3\u30fc\u30eb\u30c9\u306b\u30c7\u30d5\u30a9\u30eb\u30c8\u5024\u3092\u6307\u5b9a\u3057\u3066\u3001\u30d5\u30a9\u30fc\u30e0\u3067\u53ce\u96c6\u3059\u308b\u30c7\u30fc\u30bf\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u4f5c\u6210\u3057\u307e\u3059\u3002\u305d\u3057\u3066\u3001<code>useState<\/code>\u3092\u4f7f\u3063\u3066<code>formData<\/code>\u306estate\u3092\u521d\u671f\u5316\u3057\u307e\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">let formStateData = {\n    firstName: '',\n    lastName: '',\n    email: '',\n};\n\nconst [formData, setFormData] = useState(formStateData);<\/code><\/pre>\n<p>\u6b21\u306b\u3001\u30d5\u30a9\u30fc\u30e0\u30d5\u30a3\u30fc\u30eb\u30c9\u304c\u5909\u66f4\u3055\u308c\u308b\u305f\u3073\u306b<code>formData<\/code>\u306estate\u3092\u66f4\u65b0\u3059\u308b<code>handleInputChange<\/code>\u95a2\u6570\u3092\u5b9a\u7fa9\u3057\u307e\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">const handleInputChange = (event) =&gt; {\n    const { name, value } = event.target;\n    setFormData({ ...formData, [name]: value });\n};<\/code><\/pre>\n<p>\u6700\u5f8c\u306b\u3001\u30d5\u30a9\u30fc\u30e0\u304c\u9001\u4fe1\u3055\u308c\u305f\u3068\u304d\u306b\u73fe\u5728\u306e\u30d5\u30a9\u30fc\u30e0\u30c7\u30fc\u30bf\u3092\u30b3\u30f3\u30bd\u30fc\u30eb\u306b\u30ed\u30b0\u51fa\u529b\u3059\u308b<code>handleSubmit<\/code>\u95a2\u6570\u3092\u5b9a\u7fa9\u3057\u307e\u3059\u3002<\/p>\n<pre><code class=\"language-jsx\">const handleSubmit = (event) =&gt; {\n    event.preventDefault();\n    console.log(formData);\n};<\/code><\/pre>\n<h2>useState\u306e\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9<\/h2>\n<p><code>useState<\/code>\u30d5\u30c3\u30af\u3092\u4f7f\u7528\u3059\u308b\u969b\u306b\u306f\u3001\u3088\u304f\u3042\u308b\u9593\u9055\u3044\u3092\u907f\u3051\u3001\u6700\u9069\u306a\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u78ba\u4fdd\u3059\u308b\u305f\u3081\u306b\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9\u306b\u5f93\u3046\u3053\u3068\u304c\u91cd\u8981\u3067\u3059\u3002\u4ee5\u4e0b\u306b\u3001\u899a\u3048\u3066\u304a\u304f\u3079\u304d\u3044\u304f\u3064\u304b\u306e\u30d2\u30f3\u30c8\u3092\u3054\u7d39\u4ecb\u3057\u307e\u3059\u3002<\/p>\n<ul>\n<li><strong>\u6df1\u3044\u30cd\u30b9\u30c8\u306f\u907f\u3051\u308b<\/strong>\uff1a\u8907\u96d1\u306astate\u30c7\u30fc\u30bf\u3092\u3072\u3068\u3064\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306b\u683c\u7d0d\u3059\u308b\u306e\u3067\u306f\u306a\u304f\u3001\u7d30\u304b\u304f\u5206\u5272\u3057\u3066\u7ba1\u7406\u3057\u3084\u3059\u304f\u3057\u307e\u3057\u3087\u3046\u3002<\/li>\n<li><strong>\u95a2\u6570\u3092\u4f7f\u3063\u3066\u66f4\u65b0\u3092\u884c\u3046<\/strong>\uff1a\u4ee5\u524d\u306estate\u306b\u57fa\u3065\u3044\u3066state\u3092\u66f4\u65b0\u3059\u308b\u5834\u5408\u306f\u3001\u7af6\u5408\u72b6\u614b\u3092\u56de\u907f\u3057\u3001\u6b63\u3057\u304fstate\u304c\u66f4\u65b0\u3055\u308c\u308b\u3088\u3046\u306b\u3001\u95a2\u6570\u3092\u4f7f\u7528\u3067\u304d\u307e\u3059\u3002<\/li>\n<li><strong>\u904e\u5270\u306astate\u306e\u66f4\u65b0\u3092\u907f\u3051\u308b<\/strong>\uff1astate\u306e\u66f4\u65b0\u306b\u306f\u30b3\u30b9\u30c8\u304c\u304b\u304b\u308b\u306e\u3067\u3001\u305d\u306e\u56de\u6570\u3092\u6700\u5c0f\u9650\u306b\u6291\u3048\u308b\u3088\u3046\u306b\u3057\u307e\u3057\u3087\u3046\u3002<code>useEffect<\/code><a href=\"https:\/\/kinsta.com\/jp\/blog\/react-useeffect\/\">\u30d5\u30c3\u30af<\/a>\u3092\u4f7f\u7528\u3057\u3066\u66f4\u65b0\u3092\u30d0\u30c3\u30c1\u5316\u3057\u3001\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u6700\u9069\u5316\u3059\u308b\u3053\u3068\u3092\u691c\u8a0e\u3057\u307e\u3057\u3087\u3046\u3002<\/li>\n<li><strong>\u4e0d\u5fc5\u8981\u306a\u518d\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0\u3092\u907f\u3051\u308b<\/strong>\uff1aReact\u306f\u3001\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u306estate\u3084props\u304c\u5909\u66f4\u3055\u308c\u308b\u305f\u3073\u306b\u518d\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0\u3057\u307e\u3059\u3002\u4e0d\u8981\u306a\u518d\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0\u3092\u907f\u3051\u308b\u306b\u306f\u3001memo\u95a2\u6570\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/li>\n<\/ul>\n\n<h2>\u307e\u3068\u3081<\/h2>\n<p>\u3053\u306e\u8a18\u4e8b\u3067\u306f\u3001<code>useState<\/code>\u30d5\u30c3\u30af\u306b\u3064\u3044\u3066\u8a73\u3057\u304f\u8aac\u660e\u3057\u3001\u95a2\u6570\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u306bstate\u3092\u8ffd\u52a0\u3059\u308b\u65b9\u6cd5\u3092\u3054\u7d39\u4ecb\u3057\u307e\u3057\u305f\u3002\u307e\u305f\u3001<code>useState<\/code>\u3092\u30d5\u30a9\u30fc\u30e0\u3001\u914d\u5217\u3001\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3067\u4f7f\u7528\u3059\u308b\u65b9\u6cd5\u3092\u6271\u3044\u3001\u6700\u9069\u306a\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u5b9f\u73fe\u3059\u308b\u305f\u3081\u306e\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9\u306b\u3064\u3044\u3066\u3082\u53d6\u308a\u4e0a\u3052\u307e\u3057\u305f\u3002\u3053\u306e\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9\u306b\u5f93\u3046\u3053\u3068\u3067\u3001React\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u3092\u52b9\u7387\u7684\u3067\u30b9\u30b1\u30fc\u30e9\u30d6\u30eb\u3001\u304b\u3064\u4fdd\u5b88\u3057\u3084\u3059\u3044\u3082\u306e\u306b\u4fdd\u3064\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n<p>React\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u306b\u3074\u3063\u305f\u308a\u306e\u30b5\u30fc\u30d0\u30fc\u3092\u304a\u63a2\u3057\u3067\u3042\u308c\u3070\u3001<a href=\"https:\/\/sevalla.com\/application-hosting\/\">Kinsta\u306e\u30a6\u30a7\u30d6\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u30b5\u30fc\u30d0\u30fc<\/a>\u3092\u307e\u305a\u306f\u7121\u6599\u304b\u3089\u304a\u8a66\u3057\u304f\u3060\u3055\u3044\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>React\u306f\u3001\u30e6\u30fc\u30b6\u30fc\u30a4\u30f3\u30bf\u30fc\u30d5\u30a7\u30fc\u30b9\u306e\u69cb\u7bc9\u306b\u4f7f\u7528\u3055 &#8230;<\/p>\n","protected":false},"author":287,"featured_media":46772,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_kinsta_gated_content":false,"_kinsta_gated_content_redirect":"","footnotes":""},"tags":[],"topic":[802],"class_list":["post-46771","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","topic-react"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v24.6 (Yoast SEO v24.6) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>React\u3067useState\u30d5\u30c3\u30af\u306e\u5229\u7528\u3092\u958b\u59cb\u3059\u308b\uff5cKinsta\u00ae<\/title>\n<meta name=\"description\" content=\"useState\u30d5\u30c3\u30af\u3067React\u30a2\u30d7\u30ea\u3092\u30d1\u30ef\u30fc\u30a2\u30c3\u30d7\u3002\u521d\u5fc3\u8005\u5411\u3051\u306e\u89e3\u8aac\u3068\u3057\u3066\u3001React\u306euseState\u7ba1\u7406\u306b\u3064\u3044\u3066\u77e5\u3063\u3066\u304a\u304f\u3079\u304d\u57fa\u672c\u3092\u3054\u7d39\u4ecb\u3057\u307e\u3059\u3002\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/kinsta.com\/jp\/blog\/usestate-react\/\" \/>\n<meta property=\"og:locale\" content=\"ja_JP\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"React\u3067useState\u30d5\u30c3\u30af\u306e\u5229\u7528\u3092\u958b\u59cb\u3059\u308b\" \/>\n<meta property=\"og:description\" content=\"useState\u30d5\u30c3\u30af\u3067React\u30a2\u30d7\u30ea\u3092\u30d1\u30ef\u30fc\u30a2\u30c3\u30d7\u3002\u521d\u5fc3\u8005\u5411\u3051\u306e\u89e3\u8aac\u3068\u3057\u3066\u3001React\u306euseState\u7ba1\u7406\u306b\u3064\u3044\u3066\u77e5\u3063\u3066\u304a\u304f\u3079\u304d\u57fa\u672c\u3092\u3054\u7d39\u4ecb\u3057\u307e\u3059\u3002\" \/>\n<meta property=\"og:url\" content=\"https:\/\/kinsta.com\/jp\/blog\/usestate-react\/\" \/>\n<meta property=\"og:site_name\" content=\"Kinsta\u00ae\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/Kinsta-Japan-334616080691171\/\" \/>\n<meta property=\"article:published_time\" content=\"2023-11-13T09:20:16+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-10-01T19:45:44+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/kinsta.com\/jp\/wp-content\/uploads\/sites\/6\/2023\/06\/usestate-react.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1460\" \/>\n\t<meta property=\"og:image:height\" content=\"730\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"Joel Olawanle\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:description\" content=\"useState\u30d5\u30c3\u30af\u3067React\u30a2\u30d7\u30ea\u3092\u30d1\u30ef\u30fc\u30a2\u30c3\u30d7\u3002\u521d\u5fc3\u8005\u5411\u3051\u306e\u89e3\u8aac\u3068\u3057\u3066\u3001React\u306euseState\u7ba1\u7406\u306b\u3064\u3044\u3066\u77e5\u3063\u3066\u304a\u304f\u3079\u304d\u57fa\u672c\u3092\u3054\u7d39\u4ecb\u3057\u307e\u3059\u3002\" \/>\n<meta name=\"twitter:image\" content=\"https:\/\/kinsta.com\/jp\/wp-content\/uploads\/sites\/6\/2023\/06\/usestate-react.jpg\" \/>\n<meta name=\"twitter:creator\" content=\"@olawanle_joel\" \/>\n<meta name=\"twitter:site\" content=\"@Kinsta_JP\" \/>\n<meta name=\"twitter:label1\" content=\"\u57f7\u7b46\u8005\" \/>\n\t<meta name=\"twitter:data1\" content=\"Joel Olawanle\" \/>\n\t<meta name=\"twitter:label2\" content=\"\u63a8\u5b9a\u8aad\u307f\u53d6\u308a\u6642\u9593\" \/>\n\t<meta name=\"twitter:data2\" content=\"3\u5206\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/kinsta.com\/jp\/blog\/usestate-react\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/kinsta.com\/jp\/blog\/usestate-react\/\"},\"author\":{\"name\":\"Joel 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