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\r\nfunction foo(){\r\n for(var a=0;a<10;a++){}\r\n console.log(a);\/\/10\r\n for(a=0;a<10;a++){}\r\n}\r\nfoo();\r\n<\/pre>\n\r\nfunction foo(){\r\n (function(){\r\n for(var a=0;a<10;a++){}\r\n })();\r\n console.log(a);\/\/undefined\r\n}\r\nfoo();\r\n<\/pre>\n\u7136\u800ces2015\u7ed9\u4f60\u63d0\u4f9b\u4e86\u66f4\u597d\u7684\u65b9\u6848:<\/p>\n
\r\nfunction foo(){\r\n "use strict";\r\n for(let a=0;a<10;a++){}\r\n console.log(a); \/\/undefined\r\n}\r\nfoo();\r\n<\/pre>\n\u4f46\u5199\u672c\u6587\u7684\u4e3b\u8981\u76ee\u7684\u4e0e\u4e0a\u9762\u7684\u5173\u7cfb\u4e0d\u662f\u592a\u5927,\u672c\u6587\u4e3b\u8981\u60f3\u63a2\u7a76\u51fd\u6570\u7ea7\u7684\u4f5c\u7528\u57df\u95ee\u9898<\/p>\n
\r\nfunction foo(){\r\n var a=0;\r\n function b(){\r\n console.log('b');\r\n }\r\n function bar(){\r\n console.log(a);\/\/a\r\n b();\/\/b\r\n }\r\n bar();\r\n}\r\nfoo();\r\n<\/pre>\n\u6267\u884c\u8fd9\u4e00\u6bb5\u7a0b\u5e8f\u4e4b\u540e\u53ef\u4ee5\u53d1\u73b0\u51fd\u6570\u91cc\u7684\u6240\u6709\u53d8\u91cf\u548c\u51fd\u6570\u662f\u53ef\u4ee5\u88ab\u8be5\u51fd\u6570\u4ee5\u53ca\u8be5\u51fd\u6570\u5185\u90e8\u7684\u5b50\u51fd\u6570\u6240\u8bbf\u95ee\u7684,\u7a0d\u5fae\u6539\u4e00\u4e0b\u4ee3\u7801<\/p>\n
\r\nfunction foo(){\r\n var a=0;\r\n function b(){\r\n console.log('b');\r\n }\r\n function bar(){\r\n console.log(a);\/\/a\r\n b();\/\/b\r\n }\r\n bar.call(d);\r\n}\r\nfunction d(){\r\n}\r\nfoo();\r\n<\/pre>\n\u53d1\u73b0\u8f93\u51fa\u7684\u7ed3\u679c\u662f\u76f8\u540c\u7684,\u4e0a\u9762\u8fd9\u4e2a\u4f8b\u5b50\u662f\u4e3a\u4e86\u8bc1\u660e\u89e3\u91ca\u5668\u5728\u67e5\u627e\u53d8\u91cf\u7684\u65f6\u5019\u4e0d\u662f\u901a\u8fc7this\u5b9a\u4f4d\u67e5\u627e\u7684,\u56e0\u4e3a\u5728\u7b2c\u4e00\u4e2a\u4f8b\u5b50\u4e2dthis\u4e3awindow(strict mode \u4e3aundefined),\u7b2c\u4e8c\u4e2a\u4f8b\u5b50\u4e2d\u4e3ad\u51fd\u6570,\u8fd9\u4e2a\u73b0\u8c61\u7684\u5177\u4f53\u539f\u56e0\u53ef\u4ee5\u901a\u8fc7\u89c2\u5bdf\u5b9e\u9645\u7684\u4f5c\u7528\u57df\u94fe\u53bb\u89e3\u91ca.
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\r\nfunction Foo(){\r\n var a=1;\r\n this.a=2;\r\n function geta(){\r\n "use strict";\r\n console.log(a); \/\/1\r\n console.log(this.a); \/\/Cannot read property 'a' of undefined\r\n }\r\n this.geta=function(){\r\n console.log(a);\/\/1\r\n console.log(this.a);\/\/2\r\n }\r\n geta();\r\n}\r\nfoo=new Foo();\r\nfoo.geta();\r\n<\/pre>\n\u603b\u4f53\u6765\u8bf4,\u53ef\u4ee5\u7b80\u5355\u6982\u62ec\u6210\u4e00\u53e5\u8bdd:this\u662fthis,\u4f5c\u7528\u57df\u662f\u4f5c\u7528\u57df.\u4e0d\u80fd\u5c06this\u548c\u4f5c\u7528\u57df\u6df7\u6dc6,\u8fd9\u6837\u4ee5\u6765\u54ea\u4e9b\u53ef\u4ee5\u8bbf\u95ee\u5230,\u54ea\u4e9b\u4e0d\u80fd\u88ab\u8bbf\u95ee,\u5f88\u5bb9\u6613\u5c31\u80fd\u533a\u5206\u51fa\u6765,\u4e5f\u80fd\u5f88\u5feb\u7406\u89e3\u4e3a\u5565\u597d\u591a\u5176\u4ed6\u4eba\u5199\u7684\u7a0b\u5e8f\u91cc\u9762\u4f1a\u51fa\u73b0apply\u6216call,\u8fd9\u80af\u5b9a\u662f\u56e0\u4e3a\u91cc\u9762\u7528\u5230\u4e86this,\u800c\u548c\u4f5c\u7528\u57df\u5c31\u626f\u4e0d\u4e0a\u4efb\u4f55\u5173\u7cfb\u4e86.<\/p>\n","protected":false},"excerpt":{"rendered":"
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