{"id":198164,"date":"2020-08-17T10:22:27","date_gmt":"2020-08-17T02:22:27","guid":{"rendered":"https:\/\/lrxjmw.cn\/?p=198164"},"modified":"2020-08-10T09:23:08","modified_gmt":"2020-08-10T01:23:08","slug":"scope-of-js","status":"publish","type":"post","link":"https:\/\/lrxjmw.cn\/scope-of-js.html","title":{"rendered":"JS\u7684\u4f5c\u7528\u57df"},"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>\u4f5c\u7528\u57df\u662f\u7528\u6765\u58f0\u660e\uff0c\u8bbf\u95ee\u548c\u4fee\u6539\u53d8\u91cf\u7684\u4e0a\u4e0b\u6587\uff0c\u5b9a\u4e49\u4e86\u53d8\u91cf\u7684\u8bbf\u95ee\u6743\u9650\u548c\u67e5\u627e\u673a\u5236\u3002<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>\u4f5c\u7528\u57df\u5206\u7c7b\uff1a<\/p>\n<ul>\n<li>\u5168\u5c40\u4f5c\u7528\u57df 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\r\n<\/pre>\n<p>\u7f16\u8bd1\u8fc7\u7a0b\uff1a<\/p>\n<ul>\n<ol>\u5206\u6210var a\u3001a=1\uff1b\u4e24\u90e8\u5206\u8fdb\u884c\u5206\u6790\u3002<\/ol>\n<ol>\u67e5\u770b\u5f53\u524d\u4f5c\u7528\u57df\u662f\u5426\u6709a\uff0c\u5982\u679c\u6709\u5c31\u5ffd\u7565\uff0c\u5982\u679c\u6ca1\u6709\u5c31\u521b\u5efa\u53d8\u91cfa\u3002<\/ol>\n<ol>(var\u3001function\u58f0\u660e\u7684\u53d8\u91cf\u4f1a\u5728\u5f53\u524d\u4f5c\u7528\u57df\u4e0b\u8fdb\u884c\u53d8\u91cf\u63d0\u5347)<br \/>\n\u8d4b\u503c\u64cd\u4f5c\uff0c\u9996\u5148\u67e5\u770b\u5f53\u524d\u4f5c\u7528\u57df\u4e0b\u662f\u5426\u6709\u53d8\u91cfa\uff0c\u8981\u662f\u4e0d\u5b58\u5728\u53d8\u91cfa\u5c31\u4f1a\u62a5\u9519\uff0c\u8981\u662f\u5b58\u5728\u8fdb\u884c\u8d4b\u503c\uff1b\u5176\u6b21\u5982\u679c\u662f\u4f5c\u7528\u57df\u5d4c\u5957\u7684\u60c5\u51b5\uff0c\u5f53\u524d\u4f5c\u7528\u57df\u4e0b\u4e0d\u5b58\u5728\u53d8\u91cfa\uff0c\u5c31\u4f1a\u5411\u5916\u5c42\u4f5c\u7528\u57df\u67e5\u627e\uff0c\u76f4\u5230\u5168\u5c40\u4f5c\u7528\u57df\uff0c\u5982\u679c\u4e0d\u5b58\u5728\u53d8\u91cfa\u5c31\u4f1a\u62a5\u9519\u3002<\/ol>\n<\/ul>\n<p>\u6267\u884c\u8fc7\u7a0b\uff1a<\/p>\n<ul>\n<ol>\u6267\u884cvar a\u8bed\u53e5\u8fdb\u884c\u67e5\u627ea\u53d8\u91cf\uff0c\u8fd9\u4e2a\u8fc7\u7a0b\u53eb\u505aLHS(\u5de6\u4fa7\u4e3a\u67e5\u627e\u76ee\u6807)\u3002<\/ol>\n<ol>\u6267\u884ca = 1\u8d4b\u503c\u64cd\u4f5c\uff0c\u8fc7\u7a0b\u53eb\u505aRHS(\u53f3\u4fa7\u4e3a\u76ee\u6807\u67e5\u627e\u7684\u76ee\u7684)\u3002<\/ol>\n<ol>\u8fdb\u884cRHS\u5fc5\u7136\u4f1a\u8fdb\u884cLHS\u3002<\/ol>\n<\/ul>\n<p>\u6ce8\u610f\uff1a\u53d6\u503c\u548c\u8d4b\u503c\u90fd\u662fRHS\uff0c\u53d8\u91cf\u58f0\u660e\u548c\u5f62\u53c2\u662fLHS\uff1bRHS\u548cLHS\u53d1\u751f\u5728\u6267\u884c\u8fc7\u7a0b\u4e2d\u3002<\/p>\n<p>\u793a\u4f8b\uff1a<\/p>\n<pre>\r\nfunction foo(a) {\r\n    var b = a;\r\n    return a + b\r\n}\r\nvar c = foo(2)\r\n<\/pre>\n<p>3\u5904LHS\u67e5\u8be2\uff1a<\/p>\n<ul>\n<ol>\nvar c \u58f0\u660e<\/ol>\n<ol>\nvar b \u58f0\u660e<\/ol>\n<ol>\n\u5f62\u53c2 a \u58f0\u660e<\/ol>\n<\/ul>\n<p>4\u5904RHS\u67e5\u8be2\uff1a<\/p>\n<ul>\n<ol>\nfoo(2) \u53d6\u503cfoo\u5e76\u6267\u884c<\/ol>\n<ol>\nvar b = a\u8bed\u53e5\uff0c\u53d6\u503ca<\/ol>\n<ol>\na + b\u8bed\u53e5\uff0c\u53d6\u503ca<\/ol>\n<ol>\na + b\u8bed\u53e5\uff0c\u53d6\u503cb<\/ol>\n<\/ul>\n<p>\u7528var\u58f0\u660e\u7684\u53d8\u91cf\u4f1a\u8fdb\u884c\u53d8\u91cf\u63d0\u5347\uff0c\u63d0\u5347\u5230\u5f53\u524d\u4f5c\u7528\u57df\u7684\u6700\u9876\u90e8\uff0c\u5176\u503c\u662fundefined\uff0c\u56e0\u6b64\u5728\u53d8\u91cf\u524d\u8fdb\u884c\u53d6\u503c\u4e0d\u4f1a\u62a5\u9519\u3002<br 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