{"id":1594,"date":"2025-08-03T12:59:07","date_gmt":"2025-08-03T03:59:07","guid":{"rendered":"https:\/\/blog.espresso.earth\/?p=1594"},"modified":"2025-08-10T13:07:25","modified_gmt":"2025-08-10T04:07:25","slug":"map","status":"publish","type":"post","link":"https:\/\/blog.espresso.earth\/index.php\/2025\/08\/03\/map\/","title":{"rendered":"Javascript\u306eMap\u306b\u3064\u3044\u3066\u4f53\u7cfb\u7684\u306b\u7406\u89e3\u3059\u308b\u3002"},"content":{"rendered":"\n

JavaScript \u306e Map<\/code> \u3092\u4f53\u7cfb\u7684\u306b\u7406\u89e3\u3059\u308b<\/h2>\n\n\n\n

\u306f\u3058\u3081\u306b<\/p>\n\n\n\n

Javascript\u3092\u4f7f\u7528\u3057\u3066\u3044\u3066\u3001\u7406\u89e3\u304c\u66d6\u6627\u3060\u3063\u305f\u7b87\u6240\u304c\u3042\u308a\u3001\uff11\u304b\u3089\u5b66\u3073\u306a\u304a\u3059\u3053\u3068\u306b\u3057\u307e\u3057\u305f\u3002<\/p>\n\n\n\n

Map\u3068\u3044\u3046\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u4f7f\u3048\u3070\u30011:1\u306e\u30c7\u30fc\u30bf\u69cb\u9020\u3092\u7c21\u5358\u306b\u6271\u3046\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n

C++\u3067\u8a00\u3046\u3068\u3053\u308d\u306eenum table\u306e\u3088\u3046\u306a\u4f7f\u3044\u65b9\u304c\u3067\u304d\u307e\u3059\u304c\u3001Map\u306f\u72ec\u81ea\u306b\u30e1\u30bd\u30c3\u30c9\u3092\u6301\u3063\u3066\u304a\u308a\u3001<\/p>\n\n\n\n

C++\u3067\u8a00\u3046\u3068\u3053\u308d\u306estd::vector\u306a\u3069\u306e\u6301\u3064\u914d\u5217\u64cd\u4f5c\u7528\u306e\u30e1\u30bd\u30c3\u30c9\u306b\u8fd1\u3044\u4f7f\u7528\u611f\u3067\u51e6\u7406\u3092\u66f8\u304f\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n

1. \u6982\u8981<\/h3>\n\n\n\n

Map<\/code> \u306f\u300c\u30ad\u30fc\u3068\u5024\u306e\u30da\u30a2\u300d\u3092\u4fdd\u6301\u3059\u308b\u7d44\u307f\u8fbc\u307f\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3067\u3059\u3002
\u4e3b\u306a\u7279\u5fb4\u306f\u4ee5\u4e0b\u3067\u3059\uff1a<\/p>\n\n\n\n

    \n
  • \u4efb\u610f\u306e\u578b\u306e\u5024\u3092\u30ad\u30fc\u306b\u3067\u304d\u308b<\/strong>\uff08\u6587\u5b57\u5217\u3001\u6570\u5024\u3001\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3001\u95a2\u6570\u3001\u30b7\u30f3\u30dc\u30eb\u306a\u3069\uff09<\/li>\n\n\n\n
  • \u30ad\u30fc\u306e\u633f\u5165\u9806\u5e8f\u3092\u4fdd\u6301<\/strong>\u3059\u308b<\/li>\n\n\n\n
  • \u30b5\u30a4\u30ba\u3092 O(1) \u3067\u53d6\u5f97\u3067\u304d\u308b<\/strong>\uff08.size<\/code> \u30d7\u30ed\u30d1\u30c6\u30a3\uff09<\/li>\n\n\n\n
  • \u53cd\u5fa9\u53ef\u80fd\uff08iterable\uff09<\/strong> \u306a\u306e\u3067 for...of<\/code> \u3084\u30b9\u30d7\u30ec\u30c3\u30c9\u69cb\u6587\u3067\u5c55\u958b\u53ef\u80fd<\/li>\n<\/ul>\n\n\n\n
    \n\n\n\n

    2. \u57fa\u672c\u69cb\u6587\u3068\u4e3b\u8981\u30e1\u30bd\u30c3\u30c9<\/h3>\n\n\n\n
    \/\/ \u4f5c\u6210\nconst map = new Map();\n\n\/\/ set(key, value) - \u8ffd\u52a0\u307e\u305f\u306f\u66f4\u65b0\nmap.set('x', 10);\nmap.set('y', 20);\n\n\/\/ get(key) - \u5024\u306e\u53d6\u5f97\uff08\u306a\u3051\u308c\u3070 undefined\uff09\nconsole.log(map.get('x')); \/\/ 10\nconsole.log(map.get('z')); \/\/ undefined\n\n\/\/ has(key) - \u30ad\u30fc\u304c\u5b58\u5728\u3059\u308b\u304b\uff1f\nconsole.log(map.has('y')); \/\/ true\n\n\/\/ delete(key) - \u30a8\u30f3\u30c8\u30ea\u524a\u9664\nmap.delete('x');\n\n\/\/ clear() - \u5168\u524a\u9664\nmap.clear();\n\n\/\/ size - \u8981\u7d20\u6570\uff08getter\u30d7\u30ed\u30d1\u30c6\u30a3\uff09\nconsole.log(map.size);\n<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    3. \u30a4\u30c6\u30ec\u30fc\u30b7\u30e7\u30f3<\/h3>\n\n\n\n
    Map<\/code> \u306f\u633f\u5165\u9806\u3067\u53cd\u5fa9\u53ef\u80fd\u3067\u3059\u3002<\/p>\n\n\n\n
    const m = new Map([\n  ['a', 1],\n  ['b', 2],\n  ['c', 3],\n]);\n\nfor (const [key, value] of m) {\n  console.log(key, value);\n}\n\n\/\/ \u5c02\u7528\u30e1\u30bd\u30c3\u30c9\nfor (const key of m.keys()) console.log('key:', key);\nfor (const value of m.values()) console.log('value:', value);\nfor (const entry of m.entries()) console.log('entry:', entry);\n<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    4. \u4ed6\u306e\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u3068\u306e\u6bd4\u8f03<\/h3>\n\n\n\n
    \u7279\u5fb4<\/th>Object<\/th>Map<\/th><\/tr><\/thead>
    \u30ad\u30fc\u306e\u578b<\/td>\u6587\u5b57\u5217 or \u30b7\u30f3\u30dc\u30eb<\/td>\u4efb\u610f\u306e\u578b\uff08\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u542b\u3080\uff09<\/td><\/tr>
    \u9806\u5e8f\u4fdd\u8a3c<\/td>\u4e00\u90e8\u898f\u5b9a\u3042\u308a\uff08\u4ed5\u69d8\u4e0a\u8907\u96d1\uff09<\/td>\u633f\u5165\u9806\u3092\u53b3\u5bc6\u306b\u4fdd\u6301<\/td><\/tr>
    \u30b5\u30a4\u30ba\u53d6\u5f97<\/td>O(n)\uff08Object.keys().length<\/code>\uff09<\/td>O(1)\uff08.size<\/code>\uff09<\/td><\/tr>
    \u30a4\u30c6\u30ec\u30fc\u30b7\u30e7\u30f3<\/td>for...in<\/code> \u3084 Object.keys<\/code><\/td>\u76f4\u63a5\u53cd\u5fa9\u53ef\u80fd<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \n\n\n\n
    5. \u5b9f\u8df5\u4f8b<\/h3>\n\n\n\n
    5-1. \u983b\u5ea6\u30ab\u30a6\u30f3\u30c8<\/h4>\n\n\n\n
    const counts = new Map();\nconst words = ['apple', 'banana', 'apple', 'orange'];\n\nfor (const w of words) {\n  counts.set(w, (counts.get(w) || 0) + 1);\n}\n\nconsole.log(counts); \/\/ Map(3) { 'apple' => 2, 'banana' => 1, 'orange' => 1 }\n<\/code><\/pre>\n\n\n\n
    5-2. \u30ad\u30e3\u30c3\u30b7\u30e5<\/h4>\n\n\n\n
    const cache = new Map();\n\nfunction heavy(n) {\n  if (cache.has(n)) return cache.get(n);\n  const result = n * n; \/\/ \u91cd\u3044\u51e6\u7406\u3068\u4eee\u5b9a\n  cache.set(n, result);\n  return result;\n}\n\nconsole.log(heavy(4)); \/\/ \u8a08\u7b97\nconsole.log(heavy(4)); \/\/ \u30ad\u30e3\u30c3\u30b7\u30e5\u304b\u3089\n<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    6. .has()<\/code> \u306e\u4ed5\u69d8<\/h3>\n\n\n\n
    .has(key)<\/code> \u306f\u30ad\u30fc\u306e\u5b58\u5728\u6709\u7121\u3092\u8fd4\u3059\u3002<\/p>\n\n\n\n
      \n
    • \u5024\u304c undefined<\/code> \u3067\u3082\u30ad\u30fc\u304c\u3042\u308c\u3070 true<\/code><\/li>\n\n\n\n
    • \u6bd4\u8f03\u306f SameValueZero\uff08NaN<\/code> \u3092\u542b\u3081\u3066\u7b49\u3057\u3044\u3068\u307f\u306a\u3059\uff09<\/li>\n<\/ul>\n\n\n\n
      const m = new Map();\nm.set('k', undefined);\nconsole.log(m.has('k')); \/\/ true\nconsole.log(m.get('k')); \/\/ undefined\n\nm.set(NaN, 'not-a-number');\nconsole.log(m.has(NaN)); \/\/ true\n<\/code><\/pre>\n\n\n\n
      \n\n\n\n
      7. \u30b7\u30ea\u30a2\u30e9\u30a4\u30ba\uff08JSON\u5316\uff09<\/h3>\n\n\n\n
      Map<\/code> \u306f\u76f4\u63a5 JSON.stringify()<\/code> \u3059\u308b\u3068\u7a7a\u30aa\u30d6\u30b8\u30a7\u30af\u30c8 {}<\/code> \u306b\u306a\u308b\u3002
      \u4fdd\u5b58\u3059\u308b\u5834\u5408\u306f\u914d\u5217\u306b\u5909\u63db\u3059\u308b\uff1a<\/p>\n\n\n\n
      const m = new Map([['a', 1], ['b', 2]]);\nconst json = JSON.stringify([...m]); \/\/ [[\"a\",1],[\"b\",2]]\nconst restored = new Map(JSON.parse(json));\n<\/code><\/pre>\n\n\n\n
      \n\n\n\n
      8. \u6ce8\u610f\u70b9<\/h3>\n\n\n\n
        \n
      • \u53c2\u7167\u6bd4\u8f03<\/strong>\uff1a\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3084\u914d\u5217\u3092\u30ad\u30fc\u306b\u3059\u308b\u3068\u304d\u306f\u540c\u4e00\u53c2\u7167\u3067\u306a\u3051\u308c\u3070\u4e00\u81f4\u3057\u306a\u3044<\/li>\n\n\n\n
      • JSON\u5909\u63db<\/strong>\uff1a\u76f4\u63a5\u306f\u3067\u304d\u306a\u3044<\/li>\n\n\n\n
      • WeakMap<\/strong>\uff1a\u30ad\u30fc\u3092\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u9650\u5b9a\u306b\u3057\u3066 GC \u3068\u9023\u52d5\u3055\u305b\u305f\u3044\u5834\u5408\u306f WeakMap \u3092\u4f7f\u3046<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"
        JavaScript \u306e Map \u3092\u4f53\u7cfb […]<\/p>\n","protected":false},"author":1,"featured_media":1596,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8,40,24],"tags":[],"class_list":["post-1594","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-it","category-javascript","category-web"],"_links":{"self":[{"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/posts\/1594","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/comments?post=1594"}],"version-history":[{"count":5,"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/posts\/1594\/revisions"}],"predecessor-version":[{"id":1602,"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/posts\/1594\/revisions\/1602"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/media\/1596"}],"wp:attachment":[{"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/media?parent=1594"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/categories?post=1594"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.espresso.earth\/index.php\/wp-json\/wp\/v2\/tags?post=1594"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}