{"id":197043,"date":"2020-08-05T09:40:47","date_gmt":"2020-08-05T01:40:47","guid":{"rendered":"https:\/\/lrxjmw.cn\/?p=197043"},"modified":"2020-07-26T14:42:08","modified_gmt":"2020-07-26T06:42:08","slug":"introduction-to-symbol","status":"publish","type":"post","link":"https:\/\/lrxjmw.cn\/introduction-to-symbol.html","title":{"rendered":"ECMA Script 6\u4e4b Symbol\u4ecb\u7ecd"},"content":{"rendered":"<table>\n<tbody>\n<tr>\n<td style=\"padding: 5px 12px; width: 25px; font-size: 22px; text-align: center; background: #E8E8E8; line-height: 30px; color: #999;\">\u5bfc\u8bfb<\/td>\n<td style=\"padding: 10px 10px 12px; line-height: 20px;\"><strong>ES6 \u5f15\u5165\u4e86\u4e00\u79cd\u65b0\u7684\u539f\u59cb\u6570\u636e\u7c7b\u578b Symbol \uff0c\u8868\u793a\u72ec\u4e00\u65e0\u4e8c\u7684\u503c\uff0c\u6700\u5927\u7684\u7528\u6cd5\u662f\u7528\u6765\u5b9a\u4e49\u5bf9\u8c61\u7684\u552f\u4e00\u5c5e\u6027\u540d\u3002<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/lrxjmw.cn\/wp-content\/uploads\/2020\/07\/2-22.png\" alt=\"\" width=\"400\" height=\"269\" class=\"aligncenter size-full wp-image-197044\" srcset=\"https:\/\/lrxjmw.cn\/wp-content\/uploads\/2020\/07\/2-22.png 400w, https:\/\/lrxjmw.cn\/wp-content\/uploads\/2020\/07\/2-22-300x202.png 300w\" sizes=\"auto, (max-width: 400px) 100vw, 400px\" \/><\/p>\n<p>ES6 \u6570\u636e\u7c7b\u578b\u9664\u4e86 Number \u3001 String \u3001 Boolean \u3001 Objec t\u3001 null \u548c undefined \uff0c\u8fd8\u65b0\u589e\u4e86 Symbol \u3002<\/p>\n<div   id="j6sjwn9j3u"    style=\"font-size: 14pt; color: white; background-color: black; border-left: red 10px solid; padding-left: 14px; margin-bottom: 20px; margin-top: 20px;\"><strong>\u57fa\u672c\u7528\u6cd5<\/strong><\/div>\n<p>Symbol \u51fd\u6570\u6808\u4e0d\u80fd\u7528 new \u547d\u4ee4\uff0c\u56e0\u4e3a Symbol \u662f\u539f\u59cb\u6570\u636e\u7c7b\u578b\uff0c\u4e0d\u662f\u5bf9\u8c61\u3002\u53ef\u4ee5\u63a5\u53d7\u4e00\u4e2a\u5b57\u7b26\u4e32\u4f5c\u4e3a\u53c2\u6570\uff0c\u4e3a\u65b0\u521b\u5efa\u7684 Symbol \u63d0\u4f9b\u63cf\u8ff0\uff0c\u7528\u6765\u663e\u793a\u5728\u63a7\u5236\u53f0\u6216\u8005\u4f5c\u4e3a\u5b57\u7b26\u4e32\u7684\u65f6\u5019\u4f7f\u7528\uff0c\u4fbf\u4e8e\u533a\u5206\u3002<\/p>\n<pre>let sy = Symbol(\"KK\");\r\nconsole.log(sy);   \/\/ Symbol(KK)\r\ntypeof(sy);        \/\/ \"symbol\"\r\n \r\n\/\/ \u76f8\u540c\u53c2\u6570 Symbol() \u8fd4\u56de\u7684\u503c\u4e0d\u76f8\u7b49\r\nlet sy1 = Symbol(\"kk\"); \r\nsy === sy1;       \/\/ false<\/pre>\n<div   id="j6sjwn9j3u"    style=\"font-size: 14pt; color: white; background-color: black; border-left: red 10px solid; padding-left: 14px; margin-bottom: 20px; margin-top: 20px;\"><strong>\u4f7f\u7528\u573a\u666f<\/strong><\/div>\n<div   id="j6sjwn9j3u"    style=\"margin-top:2em;margin-bottom:1em\"><span style=\"color:#1E1E1E;letter-spacing: 2px;border-left:#FF3030 3px solid;border-right:#FF3030 3px solid;padding-left: 8px;padding-right:8px;font-size: 12pt\"><strong>\u4f5c\u4e3a\u5c5e\u6027\u540d<\/strong><\/span><\/div>\n<p><strong>\u7528\u6cd5<\/strong><\/p>\n<p>\u7531\u4e8e\u6bcf\u4e00\u4e2a Symbol \u7684\u503c\u90fd\u662f\u4e0d\u76f8\u7b49\u7684\uff0c\u6240\u4ee5 Symbol \u4f5c\u4e3a\u5bf9\u8c61\u7684\u5c5e\u6027\u540d\uff0c\u53ef\u4ee5\u4fdd\u8bc1\u5c5e\u6027\u4e0d\u91cd\u540d\u3002<\/p>\n<pre>let sy = Symbol(\"key1\");\r\n \r\n\/\/ \u5199\u6cd51\r\nlet syObject = {};\r\nsyObject[sy] = \"kk\";\r\nconsole.log(syObject);    \/\/ {Symbol(key1): \"kk\"}\r\n \r\n\/\/ \u5199\u6cd52\r\nlet syObject = {\r\n  [sy]: \"kk\"\r\n};\r\nconsole.log(syObject);    \/\/ {Symbol(key1): \"kk\"}\r\n \r\n\/\/ \u5199\u6cd53\r\nlet syObject = {};\r\nObject.defineProperty(syObject, sy, {value: \"kk\"});\r\nconsole.log(syObject);   \/\/ {Symbol(key1): \"kk\"}<\/pre>\n<p>Symbol \u4f5c\u4e3a\u5bf9\u8c61\u5c5e\u6027\u540d\u65f6\u4e0d\u80fd\u7528.\u8fd0\u7b97\u7b26\uff0c\u8981\u7528\u65b9\u62ec\u53f7\u3002\u56e0\u4e3a.\u8fd0\u7b97\u7b26\u540e\u9762\u662f\u5b57\u7b26\u4e32\uff0c\u6240\u4ee5\u53d6\u5230\u7684\u662f\u5b57\u7b26\u4e32 sy \u5c5e\u6027\uff0c\u800c\u4e0d\u662f Symbol \u503c sy \u5c5e\u6027\u3002<\/p>\n<pre>let syObject = {};\r\nsyObject[sy] = \"kk\";\r\n \r\nsyObject[sy];  \/\/ \"kk\"\r\nsyObject.sy;   \/\/ undefined<\/pre>\n<div   id="j6sjwn9j3u"    style=\"margin-top:2em;margin-bottom:1em\"><span style=\"color:#1E1E1E;letter-spacing: 2px;border-left:#FF3030 3px solid;border-right:#FF3030 3px solid;padding-left: 8px;padding-right:8px;font-size: 12pt\"><strong>\u6ce8\u610f\u70b9<\/strong><\/span><\/div>\n<p>Symbol \u503c\u4f5c\u4e3a\u5c5e\u6027\u540d\u65f6\uff0c\u8be5\u5c5e\u6027\u662f\u516c\u6709\u5c5e\u6027\u4e0d\u662f\u79c1\u6709\u5c5e\u6027\uff0c\u53ef\u4ee5\u5728\u7c7b\u7684\u5916\u90e8\u8bbf\u95ee\u3002\u4f46\u662f\u4e0d\u4f1a\u51fa\u73b0\u5728 for...in \u3001 for...of \u7684\u5faa\u73af\u4e2d\uff0c\u4e5f\u4e0d\u4f1a\u88ab Object.keys() \u3001 Object.getOwnPropertyNames() \u8fd4\u56de\u3002\u5982\u679c\u8981\u8bfb\u53d6\u5230\u4e00\u4e2a\u5bf9\u8c61\u7684 Symbol \u5c5e\u6027\uff0c\u53ef\u4ee5\u901a\u8fc7 Object.getOwnPropertySymbols() \u548c Reflect.ownKeys() \u53d6\u5230\u3002<\/p>\n<pre>let syObject = {};\r\nsyObject[sy] = \"kk\";\r\nconsole.log(syObject);\r\n \r\nfor (let i in syObject) {\r\n  console.log(i);\r\n}    \/\/ \u65e0\u8f93\u51fa\r\n \r\nObject.keys(syObject);                     \/\/ []\r\nObject.getOwnPropertySymbols(syObject);    \/\/ [Symbol(key1)]\r\nReflect.ownKeys(syObject);                 \/\/ [Symbol(key1)]<\/pre>\n<div   id="j6sjwn9j3u"    style=\"margin-top:2em;margin-bottom:1em\"><span style=\"color:#1E1E1E;letter-spacing: 2px;border-left:#FF3030 3px solid;border-right:#FF3030 3px solid;padding-left: 8px;padding-right:8px;font-size: 12pt\"><strong>\u5b9a\u4e49\u5e38\u91cf<\/strong><\/span><\/div>\n<p>\u5728 ES5 \u4f7f\u7528\u5b57\u7b26\u4e32\u8868\u793a\u5e38\u91cf\u3002\u4f8b\u5982\uff1a<\/p>\n<pre>const COLOR_RED = \"red\";\r\nconst COLOR_YELLOW = \"yellow\";\r\nconst COLOR_BLUE = \"blue\";<\/pre>\n<p>\u4f46\u662f\u7528\u5b57\u7b26\u4e32\u4e0d\u80fd\u4fdd\u8bc1\u5e38\u91cf\u662f\u72ec\u7279\u7684\uff0c\u8fd9\u6837\u4f1a\u5f15\u8d77\u4e00\u4e9b\u95ee\u9898\uff1a<\/p>\n<pre>const COLOR_RED = \"red\";\r\nconst COLOR_YELLOW = \"yellow\";\r\nconst COLOR_BLUE = \"blue\";\r\nconst MY_BLUE = \"blue\";\r\n \r\nfunction ColorException(message) {\r\n   this.message = message;\r\n   this.name = \"ColorException\";\r\n}\r\n \r\nfunction getConstantName(color) {\r\n    switch (color) {\r\n        case COLOR_RED :\r\n            return \"COLOR_RED\";\r\n        case COLOR_YELLOW :\r\n            return \"COLOR_YELLOW \";\r\n        case COLOR_BLUE:\r\n            return \"COLOR_BLUE\";\r\n        case MY_BLUE:\r\n            return \"MY_BLUE\";         \r\n        default:\r\n            throw new ColorException(\"Can't find this color\");\r\n    }\r\n}\r\n \r\ntry {\r\n   \r\n   var color = \"green\"; \/\/ green \u5f15\u53d1\u5f02\u5e38\r\n   var colorName = getConstantName(color);\r\n} catch (e) {\r\n   var colorName = \"unknown\";\r\n   console.log(e.message, e.name); \/\/ \u4f20\u9012\u5f02\u5e38\u5bf9\u8c61\u5230\u9519\u8bef\u5904\u7406\r\n}<\/pre>\n<p>\u4f46\u662f\u4f7f\u7528 Symbol \u5b9a\u4e49\u5e38\u91cf\uff0c\u8fd9\u6837\u5c31\u53ef\u4ee5\u4fdd\u8bc1\u8fd9\u4e00\u7ec4\u5e38\u91cf\u7684\u503c\u90fd\u4e0d\u76f8\u7b49\u3002\u7528 Symbol \u6765\u4fee\u6539\u4e0a\u9762\u7684\u4f8b\u5b50\u3002<\/p>\n<pre>const COLOR_RED = Symbol(\"red\");\r\nconst COLOR_YELLOW = Symbol(\"yellow\");\r\nconst COLOR_BLUE = Symbol(\"blue\");\r\n \r\nfunction ColorException(message) {\r\n   this.message = message;\r\n   this.name = \"ColorException\";\r\n}\r\nfunction getConstantName(color) {\r\n    switch (color) {\r\n        case COLOR_RED :\r\n            return \"COLOR_RED\";\r\n        case COLOR_YELLOW :\r\n            return \"COLOR_YELLOW \";\r\n        case COLOR_BLUE:\r\n            return \"COLOR_BLUE\";\r\n        default:\r\n            throw new ColorException(\"Can't find this color\");\r\n    }\r\n}\r\n \r\ntry {\r\n   \r\n   var color = \"green\"; \/\/ green \u5f15\u53d1\u5f02\u5e38\r\n   var colorName = getConstantName(color);\r\n} catch (e) {\r\n   var colorName = \"unknown\";\r\n   console.log(e.message, e.name); \/\/ \u4f20\u9012\u5f02\u5e38\u5bf9\u8c61\u5230\u9519\u8bef\u5904\u7406\r\n}<\/pre>\n<p>Symbol \u7684\u503c\u662f\u552f\u4e00\u7684\uff0c\u6240\u4ee5\u4e0d\u4f1a\u51fa\u73b0\u76f8\u540c\u503c\u5f97\u5e38\u91cf\uff0c\u5373\u53ef\u4ee5\u4fdd\u8bc1 switch \u6309\u7167\u4ee3\u7801\u9884\u60f3\u7684\u65b9\u5f0f\u6267\u884c\u3002<\/p>\n<div   id="j6sjwn9j3u"    style=\"margin-top:2em;margin-bottom:1em\"><span style=\"color:#1E1E1E;letter-spacing: 2px;border-left:#FF3030 3px solid;border-right:#FF3030 3px solid;padding-left: 8px;padding-right:8px;font-size: 12pt\"><strong>Symbol.for()<\/strong><\/span><\/div>\n<p>Symbol.for() \u7c7b\u4f3c\u5355\u4f8b\u6a21\u5f0f\uff0c\u9996\u5148\u4f1a\u5728\u5168\u5c40\u641c\u7d22\u88ab\u767b\u8bb0\u7684 Symbol \u4e2d\u662f\u5426\u6709\u8be5\u5b57\u7b26\u4e32\u53c2\u6570\u4f5c\u4e3a\u540d\u79f0\u7684 Symbol \u503c\uff0c\u5982\u679c\u6709\u5373\u8fd4\u56de\u8be5 Symbol \u503c\uff0c\u82e5\u6ca1\u6709\u5219\u65b0\u5efa\u5e76\u8fd4\u56de\u4e00\u4e2a\u4ee5\u8be5\u5b57\u7b26\u4e32\u53c2\u6570\u4e3a\u540d\u79f0\u7684 Symbol \u503c\uff0c\u5e76\u767b\u8bb0\u5728\u5168\u5c40\u73af\u5883\u4e2d\u4f9b\u641c\u7d22\u3002<\/p>\n<pre>let yellow = Symbol(\"Yellow\");\r\nlet yellow1 = Symbol.for(\"Yellow\");\r\nyellow === yellow1;      \/\/ false\r\n \r\nlet yellow2 = Symbol.for(\"Yellow\");\r\nyellow1 === yellow2;     \/\/ true<\/pre>\n<div   id="j6sjwn9j3u"    style=\"margin-top:2em;margin-bottom:1em\"><span style=\"color:#1E1E1E;letter-spacing: 2px;border-left:#FF3030 3px solid;border-right:#FF3030 3px solid;padding-left: 8px;padding-right:8px;font-size: 12pt\"><strong>Symbol.keyFor()<\/strong><\/span><\/div>\n<p>Symbol.keyFor() \u8fd4\u56de\u4e00\u4e2a\u5df2\u767b\u8bb0\u7684 Symbol \u7c7b\u578b\u503c\u7684 key \uff0c\u7528\u6765\u68c0\u6d4b\u8be5\u5b57\u7b26\u4e32\u53c2\u6570\u4f5c\u4e3a\u540d\u79f0\u7684 Symbol \u503c\u662f\u5426\u5df2\u88ab\u767b\u8bb0\u3002<\/p>\n<pre>let yellow1 = Symbol.for(\"Yellow\");\r\nSymbol.keyFor(yellow1);    \/\/ \"Yellow\"<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>ES6 \u6570\u636e\u7c7b\u578b\u9664\u4e86 Number \u3001 String \u3001 Boolean \u3001 Objec t\u3001 null \u548c  [&hellip;]<\/p>\n","protected":false},"author":321,"featured_media":197045,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[55],"tags":[],"class_list":["post-197043","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-thread"],"acf":[],"_links":{"self":[{"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/posts\/197043","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/users\/321"}],"replies":[{"embeddable":true,"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/comments?post=197043"}],"version-history":[{"count":2,"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/posts\/197043\/revisions"}],"predecessor-version":[{"id":197051,"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/posts\/197043\/revisions\/197051"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/media\/197045"}],"wp:attachment":[{"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/media?parent=197043"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/categories?post=197043"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lrxjmw.cn\/wp-json\/wp\/v2\/tags?post=197043"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}