{"id":545,"date":"2017-02-24T14:43:55","date_gmt":"2017-02-24T06:43:55","guid":{"rendered":"http:\/\/www.qdabc.cn\/?p=545"},"modified":"2017-02-24T15:00:43","modified_gmt":"2017-02-24T07:00:43","slug":"es6%e5%ad%a6%e4%b9%a0%e4%b8%ad%e7%9a%84%e4%b8%80%e4%ba%9b%e6%80%bb%e7%bb%93","status":"publish","type":"post","link":"http:\/\/www.qdabc.cn\/?p=545","title":{"rendered":"ES6\u5b66\u4e60\u4e2d\u7684\u4e00\u4e9b\u603b\u7ed3"},"content":{"rendered":"

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\u4e00\u3001const\u547d\u4ee4<\/p>\n

1\u3001const\u58f0\u660e\u4e00\u4e2a\u53ea\u8bfb\u7684\u5e38\u91cf\u3002\u4e00\u65e6\u58f0\u660e\uff0c\u5e38\u91cf\u7684\u503c\u5c31\u4e0d\u80fd\u6539\u53d8\u3002\u6539\u53d8\u5e38\u91cf\u7684\u503c\u4f1a\u62a5\u9519\u3002\u8fd9\u610f\u5473\u7740\uff0cconst\u4e00\u65e6\u58f0\u660e\u53d8\u91cf\uff0c\u5c31\u5fc5\u987b\u7acb\u5373\u521d\u59cb\u5316\uff0c\u4e0d\u80fd\u7559\u5230\u4ee5\u540e\u8d4b\u503c\u3002
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\n3\u3001const\u547d\u4ee4\u58f0\u660e\u7684\u5e38\u91cf\u4e5f\u662f\u4e0d\u63d0\u5347\uff08\u58f0\u660e\u4e0d\u63d0\u524d\uff09\uff0c\u540c\u6837\u5b58\u5728\u6682\u65f6\u6027\u6b7b\u533a\uff0c\u53ea\u80fd\u5728\u58f0\u660e\u7684\u4f4d\u7f6e\u540e\u9762\u4f7f\u7528\u3002
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\/\/\u7247\u65ad1\r\nconst PI = 3.1415;\r\nPI \/\/ 3.1415\r\n\r\nPI = 3;\r\n\/\/ TypeError: Assignment to constant variable.\r\n\r\n\/\/\u7247\u65ad2\r\nconst foo;\r\n\/\/ SyntaxError: Missing initializer in const declaration\r\n\r\n\/\/\u7247\u65ad3\r\nif (true) {\r\n  const MAX = 5;\r\n}\r\n\r\nMAX \/\/ Uncaught ReferenceError: MAX is not defined\r\n\r\n\/\/\u7247\u65ad4\r\nif (true) {\r\n  console.log(MAX); \/\/ ReferenceError\r\n  const MAX = 5;\r\n}\r\n\r\n\/\/\u7247\u65ad5\r\nvar message = \"Hello!\";\r\nlet age = 25;\r\n\r\n\/\/ \u4ee5\u4e0b\u4e24\u884c\u90fd\u4f1a\u62a5\u9519\r\nconst message = \"Goodbye!\";\r\nconst age = 30;<\/pre>\n
5\u3001\u5bf9\u4e8e\u590d\u5408\u7c7b\u578b\u7684\u53d8\u91cf\uff0c\u53d8\u91cf\u540d\u4e0d\u6307\u5411\u6570\u636e\uff0c\u800c\u662f\u6307\u5411\u6570\u636e\u6240\u5728\u7684\u5730\u5740\u3002
\nconst\u547d\u4ee4\u53ea\u662f\u4fdd\u8bc1\u53d8\u91cf\u540d\u6307\u5411\u7684\u5730\u5740\u4e0d\u53d8\uff0c\u5e76\u4e0d\u4fdd\u8bc1\u8be5\u5730\u5740\u7684\u6570\u636e\u4e0d\u53d8\uff0c\u6240\u4ee5\u5c06\u4e00\u4e2a\u5bf9\u8c61\u58f0\u660e\u4e3a\u5e38\u91cf\u5fc5\u987b\u975e\u5e38\u5c0f\u5fc3\u3002
\n\u590d\u5408\u7c7b\u578b\uff1a
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\n\u5e38\u7528\u7684\u5982\uff1aArray\uff08\u6570\u7ec4\uff09\u3001Object\uff08\u5bf9\u8c61\uff09\u3001Date\uff08\u65e5\u671f\uff09\u3001Math\uff08\u6570\u5b66\u5f0f\uff09\u3001RegExp\uff08\u6b63\u5219\u8868\u8fbe\u5f0f\uff09\u3001function\uff08\u51fd\u6570\uff09<\/p>\n
const foo = {};\r\nfoo.prop = 123;\r\n\r\nfoo.prop\r\n\/\/ 123\r\n\r\nfoo = {}; \/\/ TypeError: \"foo\" is read-only\r\n\r\n\/\/\u4e0a\u9762\u4ee3\u7801\u4e2d\uff0c\u5e38\u91cffoo\u50a8\u5b58\u7684\u662f\u4e00\u4e2a\u5730\u5740\uff0c\u8fd9\u4e2a\u5730\u5740\u6307\u5411\u4e00\u4e2a\u5bf9\u8c61\u3002\r\n\/\/\u4e0d\u53ef\u53d8\u7684\u53ea\u662f\u8fd9\u4e2a\u5730\u5740\uff0c\u5373\u4e0d\u80fd\u628afoo\u6307\u5411\u53e6\u4e00\u4e2a\u5730\u5740\uff0c\u4f46\u5bf9\u8c61\u672c\u8eab\u662f\u53ef\u53d8\u7684\uff0c\u6240\u4ee5\u4f9d\u7136\u53ef\u4ee5\u4e3a\u5176\u6dfb\u52a0\u65b0\u5c5e\u6027\u3002\r\n\r\nconst a = [];\r\na.push('Hello'); \/\/ \u53ef\u6267\u884c\r\na.length = 0;    \/\/ \u53ef\u6267\u884c\r\na = ['Dave'];    \/\/ \u62a5\u9519\r\n\/\/\u4e0a\u9762\u4ee3\u7801\u4e2d\uff0c\u5e38\u91cfa\u662f\u4e00\u4e2a\u6570\u7ec4\uff0c\u8fd9\u4e2a\u6570\u7ec4\u672c\u8eab\u662f\u53ef\u5199\u7684\uff0c\u4f46\u662f\u5982\u679c\u5c06\u53e6\u4e00\u4e2a\u6570\u7ec4\u8d4b\u503c\u7ed9a\uff0c\u5c31\u4f1a\u62a5\u9519\u3002<\/pre>\n
6\u3001\u5bf9\u8c61\u51bb\u7ed3
\n\u51bb\u7ed3\u5bf9\u8c61\u5206\u4e3a1\u3001\u5bf9\u8c61\u51bb\u7ed3\uff08\u5bf9\u8c61\u4e0d\u80fd\u518d\u6dfb\u52a0\u5c5e\u6027 Object.freeze\uff09\uff1b2\u3001\u5f7b\u5e95\u51bb\u7ed3\uff08\u9664\u4e86\u5c06\u5bf9\u8c61\u672c\u8eab\u51bb\u7ed3\uff0c\u5bf9\u8c61\u7684\u5c5e\u6027\u4e5f\u5e94\u8be5\u51bb\u7ed3\u3002\uff09\u3002<\/p>\n
const foo = Object.freeze({});\r\n\r\n\/\/ \u5e38\u89c4\u6a21\u5f0f\u65f6\uff0c\u4e0b\u9762\u4e00\u884c\u4e0d\u8d77\u4f5c\u7528\uff1b\r\n\/\/ \u4e25\u683c\u6a21\u5f0f\u65f6\uff0c\u8be5\u884c\u4f1a\u62a5\u9519\r\nfoo.prop = 123;\r\n\r\n\r\n\/\/\u5f7b\u5e95\u51bb\u7ed3\r\nvar constantize = (obj) => {\r\n  Object.freeze(obj);\r\n  Object.keys(obj).forEach( (key, value) => {\r\n    if ( typeof obj[key] === 'object' ) {\r\n      constantize( obj[key] );\r\n    }\r\n  });\r\n};<\/pre>\n
\u4e8c\u3001ES6\u76846\u79cd\u58f0\u660e\u65b9\u6cd5
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\n4\u3001const\u547d\u4ee4
\n5\u3001import\u547d\u4ee4
\n6\u3001class\u547d\u4ee4<\/p>\n
\u4e09\u3001\u9876\u5c42\u5bf9\u8c61\u7684\u5c5e\u6027
\n\u9876\u5c42\u5bf9\u8c61\uff0c\u5728\u6d4f\u89c8\u5668\u73af\u5883\u6307\u7684\u662fwindow\u5bf9\u8c61\uff0c\u5728Node\u6307\u7684\u662fglobal\u5bf9\u8c61\u3002ES5\u4e4b\u4e2d\uff0c\u9876\u5c42\u5bf9\u8c61\u7684\u5c5e\u6027\u4e0e\u5168\u5c40\u53d8\u91cf\u662f\u7b49\u4ef7\u7684\u3002
\nES6\u4e3a\u4e86\u4fdd\u6301\u517c\u5bb9\u6027\uff0cvar\u547d\u4ee4\u548cfunction\u547d\u4ee4\u58f0\u660e\u7684\u5168\u5c40\u53d8\u91cf\uff0c\u4f9d\u65e7\u662f\u9876\u5c42\u5bf9\u8c61\u7684\u5c5e\u6027\uff1b\u53e6\u4e00\u65b9\u9762\u89c4\u5b9a\uff0clet\u547d\u4ee4\u3001const\u547d\u4ee4\u3001
\nclass\u547d\u4ee4\u58f0\u660e\u7684\u5168\u5c40\u53d8\u91cf\uff0c\u4e0d\u5c5e\u4e8e\u9876\u5c42\u5bf9\u8c61\u7684\u5c5e\u6027\u3002\u4e5f\u5c31\u662f\u8bf4\uff0c\u4eceES6\u5f00\u59cb\uff0c\u5168\u5c40\u53d8\u91cf\u5c06\u9010\u6b65\u4e0e\u9876\u5c42\u5bf9\u8c61\u7684\u5c5e\u6027\u8131\u94a9\u3002<\/p>\n
var a = 1;\r\n\/\/ \u5982\u679c\u5728Node\u7684REPL\u73af\u5883\uff0c\u53ef\u4ee5\u5199\u6210global.a\r\n\/\/ \u6216\u8005\u91c7\u7528\u901a\u7528\u65b9\u6cd5\uff0c\u5199\u6210this.a\r\nwindow.a \/\/ 1\r\n\r\nlet b = 1;\r\nwindow.b \/\/ undefined\r\n\r\n\/\/\u4e0a\u9762\u4ee3\u7801\u4e2d\uff0c\u5168\u5c40\u53d8\u91cfa\u7531var\u547d\u4ee4\u58f0\u660e\uff0c\u6240\u4ee5\u5b83\u662f\u9876\u5c42\u5bf9\u8c61\u7684\u5c5e\u6027\uff1b\r\n\/\/\u5168\u5c40\u53d8\u91cfb\u7531let\u547d\u4ee4\u58f0\u660e\uff0c\u6240\u4ee5\u5b83\u4e0d\u662f\u9876\u5c42\u5bf9\u8c61\u7684\u5c5e\u6027\uff0c\u8fd4\u56deundefined\u3002<\/pre>\n
\u56db\u3001global \u5bf9\u8c61
\n\u8fd9\u4e2a\u6682\u65f6\u6ca1\u6709\u770b\u61c2\uff0c\u53ea\u77e5\u9053\uff0c
\nES5\u7684\u9876\u5c42\u5bf9\u8c61\uff0c\u672c\u8eab\u4e5f\u662f\u4e00\u4e2a\u95ee\u9898\uff0c\u56e0\u4e3a\u5b83\u5728\u5404\u79cd\u5b9e\u73b0\u91cc\u9762\u662f\u4e0d\u7edf\u4e00\u7684\u3002<\/p>\n
\u6d4f\u89c8\u5668\u91cc\u9762\uff0c\u9876\u5c42\u5bf9\u8c61\u662fwindow\uff0c\u4f46 Node \u548c Web Worker \u6ca1\u6709window\u3002
\n\u6d4f\u89c8\u5668\u548c Web Worker \u91cc\u9762\uff0cself\u4e5f\u6307\u5411\u9876\u5c42\u5bf9\u8c61\uff0c\u4f46\u662fNode\u6ca1\u6709self\u3002
\nNode \u91cc\u9762\uff0c\u9876\u5c42\u5bf9\u8c61\u662fglobal\uff0c\u4f46\u5176\u4ed6\u73af\u5883\u90fd\u4e0d\u652f\u6301\u3002
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\u6b22\u8fce\u5206\u4eab\u672c\u6587\uff0c\u8f6c\u8f7d\u8bf7\u4fdd\u7559\u51fa\u5904\uff1a\u524d\u7aefABC<\/a> » ES6\u5b66\u4e60\u4e2d\u7684\u4e00\u4e9b\u603b\u7ed3<\/a><\/p>","protected":false},"excerpt":{"rendered":"
\u5b66\u4e60\u7684\u9053\u8def\u4e0d\u80fd\u505c\u6b62\uff0c\u60f3\u8981\u4e0d\u88ab\u6dd8\u6c70\u5c31\u8981\u4e0d\u65ad\u5730\u5b66\u4e60\u3002\u6700\u8fd1\u8bfb\u4e86\u962e\u4e00\u5cf0\u5927\u795e\u7684\u300aECMAScript 6\u5165\u95e8\u300b\u4e00\u4e66\uff0c\u5b66\u4e60\u6536\u83b7\u5f88\u5927\uff0c\u6240\u4ee5\u7279\u6b64\u505a\u4e00\u4e0b\u7b14\u8bb0\u3002 \u4e00\u3001const\u547d\u4ee4 1\u3001const\u58f0\u660e\u4e00\u4e2a\u53ea\u8bfb\u7684\u5e38\u91cf\u3002\u4e00\u65e6 […]<\/p>\n","protected":false},"author":1,"featured_media":317,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[143,144],"_links":{"self":[{"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=\/wp\/v2\/posts\/545"}],"collection":[{"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=545"}],"version-history":[{"count":3,"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=\/wp\/v2\/posts\/545\/revisions"}],"predecessor-version":[{"id":549,"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=\/wp\/v2\/posts\/545\/revisions\/549"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=\/wp\/v2\/media\/317"}],"wp:attachment":[{"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=545"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=545"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.qdabc.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=545"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}