{"id":325,"date":"2018-12-28T00:50:20","date_gmt":"2018-12-27T16:50:20","guid":{"rendered":"https:\/\/wp.winter-weng.cc\/work\/?p=325"},"modified":"2018-12-28T00:50:20","modified_gmt":"2018-12-27T16:50:20","slug":"ch-7-this-%e7%8f%be%e5%9c%a8%e5%85%a8%e9%83%bd%e8%aa%aa%e5%be%97%e9%80%9a%e4%ba%86%ef%bc%81","status":"publish","type":"post","link":"https:\/\/wp.winter-weng.cc\/work\/?p=325","title":{"rendered":"Ch. 7 this \u73fe\u5728\u5168\u90fd\u8aaa\u5f97\u901a\u4e86\uff01"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_75 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"\u986f\u793a\/\u96b1\u85cf\u5167\u5bb9\u76ee\u9304\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E5%91%BC%E5%8F%AB%E5%9C%B0%E9%BB%9E\" >\u547c\u53eb\u5730\u9ede<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E4%B8%8D%E9%81%8E%E5%B0%B1%E6%98%AF%E8%A6%8F%E5%89%87\" >\u4e0d\u904e\u5c31\u662f\u898f\u5247<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E9%A0%90%E8%A8%AD%E7%B9%AB%E7%B5%90\" >\u9810\u8a2d\u7e6b\u7d50<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E9%9A%B1%E5%90%AB%E7%9A%84%E7%B9%AB%E7%B5%90\" >\u96b1\u542b\u7684\u7e6b\u7d50<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E6%98%8E%E7%A2%BA%E7%9A%84%E7%B9%AB%E7%B5%90\" >\u660e\u78ba\u7684\u7e6b\u7d50<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E7%A1%AC%E7%B9%AB%E7%B5%90_hard_binding\" >\u786c\u7e6b\u7d50 (hard binding)<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#API_%E5%91%BC%E5%8F%AB%E7%9A%84%E3%80%8C%E6%83%85%E5%A2%83%E3%80%8D\" >API \u547c\u53eb\u7684\u300c\u60c5\u5883\u300d<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#new_%E7%B9%AB%E7%B5%90\" >new \u7e6b\u7d50<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E4%B8%80%E5%88%87%E9%83%BD%E6%8C%89%E9%A0%86%E5%BA%8F%E4%BE%86\" >\u4e00\u5207\u90fd\u6309\u9806\u5e8f\u4f86<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E7%B9%AB%E7%B5%90%E7%9A%84%E4%BE%8B%E5%A4%96\" >\u7e6b\u7d50\u7684\u4f8b\u5916<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E5%BF%BD%E7%95%A5_this\" >\u5ffd\u7565 this<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E9%96%93%E6%8E%A5%E5%8F%83%E8%80%83\" >\u9593\u63a5\u53c3\u8003<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E8%BB%9F%E5%8C%96%E7%B9%AB%E7%B5%90\" >\u8edf\u5316\u7e6b\u7d50<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E8%AA%9E%E5%BD%99%E7%9A%84_this\" >\u8a9e\u5f59\u7684 this<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-15\" href=\"https:\/\/wp.winter-weng.cc\/work\/?p=325\/#%E8%A4%87%E7%BF%92\" >\u8907\u7fd2<\/a><\/li><\/ul><\/nav><\/div>\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%91%BC%E5%8F%AB%E5%9C%B0%E9%BB%9E\"><\/span><strong>\u547c\u53eb\u5730\u9ede<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u5c0b\u627e\u547c\u53eb\u5730\u9ede\u6642\u9700\u8981\u8003\u616e\u5230\u547c\u53eb\u5806\u758a (call-stack)\u3002<br \/>\u89c0\u5bdf\u6216\u8ffd\u8e64\u5bb9\u6613\u51fa\u932f\uff0c\u53ef\u4ee5\u5229\u7528\u958b\u767c\u8005\u5de5\u5177\u5354\u52a9\u5c0b\u627e\u3002<\/p>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E4%B8%8D%E9%81%8E%E5%B0%B1%E6%98%AF%E8%A6%8F%E5%89%87\"><\/span><strong>\u4e0d\u904e\u5c31\u662f\u898f\u5247<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E9%A0%90%E8%A8%AD%E7%B9%AB%E7%B5%90\"><\/span>\u9810\u8a2d\u7e6b\u7d50<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u7576\u547c\u53eb\u662f\u666e\u901a\u7684\u53c3\u8003\uff0cthis \u6703\u6307\u5411\u5168\u57df\u3002\u56e0\u6b64 <code>this.a<\/code> \u8207 <code>var a = 2;<\/code>\uff0c\u662f\u76f8\u540c\u7684 a\u3002<\/p>\n\n\n<p>\u5728\u56b4\u683c\u6a21\u5f0f\u4e2d\uff0c\u5168\u57df\u7269\u4ef6\u4e0d\u6703\u662f\u9810\u8a2d\u7e6b\u7d50\uff0c this \u6703\u88ab\u6539\u70ba undefined\u3002<br \/>\u7576 <code>function foo()<\/code> \u5ba3\u544a\u4e0d\u8655\u65bc\u56b4\u683c\u6a21\u5f0f\u4e2d\uff0c\u4ecd\u6703\u5957\u7528\u9810\u8a2d\u7e6b\u7d50\u3002<\/p>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E9%9A%B1%E5%90%AB%E7%9A%84%E7%B9%AB%E7%B5%90\"><\/span>\u96b1\u542b\u7684\u7e6b\u7d50<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p> \u547c\u53eb\u5730\u9ede\u6709\u60c5\u5883\u7269\u4ef6 (context object) \u6642\uff0c\u8a72\u7269\u4ef6\u88ab\u4f5c\u70ba this \u7684\u53c3\u8003\u3002<br \/>obj \u5728\u51fd\u5f0f\u88ab\u547c\u53eb\u7684\u90a3\u6642\u300c\u64c1\u6709 (owns)\u300d\u6216\u300c\u5305\u542b (contains)\u300d\u51fd\u5f0f\u53c3\u8003\u3002<\/p>\n\n\n<p>\u5728\u53c3\u8003\u4e32\u93c8\u4e2d\uff0c\u53ea\u6709\u6700\u7d42\u5c64\u624d\u5c0d\u547c\u53eb\u6709\u610f\u7fa9\u3002<\/p>\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"js\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">function foo() {\n\tconsole.log( this.a );\n}\nvar obj2 = {\n\ta: 42,\n\tfoo: foo\n};\nvar obj1 = {\n\ta: 2,\n\tobj2: obj2\n};\nobj1.obj2.foo(); \/\/ 42<\/pre>\n\n\n<p><strong>\u96b1\u542b\u5730\u5931\u53bb<\/strong><\/p>\n\n\n<p>\u7576\u51fd\u5f0f\u5931\u53bb\u4e86\u7e6b\u7d50\u7684\u6642\u5019\uff0c\u4ee3\u8868\u5b83\u6703\u9000\u56de\u5230\u9810\u8a2d\u7e6b\u7d50\u3002<\/p>\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"js\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">function foo() {\n\tconsole.log( this.a );\n}\nvar obj = {\n\ta: 2,\n\tfoo: foo\n};\nvar bar = obj.foo; \/\/ function reference\/alias!\nvar a = \"oops, global\"; \/\/ `a` also property on global object\nbar(); \/\/ \"oops, global\"<\/pre>\n\n\n<p><code>bar()<\/code> \u662f\u771f\u6b63\u7684\u547c\u53eb\u5730\u9ede\uff0c\u5176\u53c3\u8003\u5230\u7684\u53ea\u662f\u4e00\u500b\u51fd\u5f0f\u7684\u4f4d\u5740\uff0c\u800c\u4e14\u662f\u666e\u901a\u3001\u672a\u7d93\u4fee\u98fe\u7684\u547c\u53eb\uff0c\u56e0\u6b64 this \u9000\u56de\u5230\u4e86\u9810\u8a2d\u7e6b\u7d50\u3002<\/p>\n\n\n<p>callback \u7d93\u5e38\u6703\u5931\u53bb this \u7e6b\u7d50\uff0c\u56e0\u70ba\u5b83\u5011\u50c5\u50c5\u662f\u5c0d\u51fd\u5f0f\u672c\u8eab\u7684\u4e00\u500b\u53c3\u8003\u3002\u800c\u6709\u4e9b\u5957\u4ef6\u6216\u51fd\u5f0f\u5eab\u53ef\u80fd\u6703\u64c5\u81ea\u4fee\u6539 this \u7684\u6307\u5411\u3002<\/p>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E6%98%8E%E7%A2%BA%E7%9A%84%E7%B9%AB%E7%B5%90\"><\/span>\u660e\u78ba\u7684\u7e6b\u7d50<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u4f7f\u7528 <code>call(..)<\/code>\u3001<code>apply(..)<\/code> \u80fd\u5920\u660e\u78ba\u5730\u6307\u5b9a this \u7684\u7e6b\u7d50\u3002<\/p>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E7%A1%AC%E7%B9%AB%E7%B5%90_hard_binding\"><\/span>\u786c\u7e6b\u7d50 (hard binding)<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u4f46\u9019\u4ecd\u7121\u6cd5\u907f\u514d\u96b1\u542b\u5730\u5931\u53bb\u6216\u662f\u7e6b\u7d50\u88ab\u5957\u4ef6\u84cb\u904e\u7684\u60c5\u6cc1\uff0c\u8981\u907f\u514d\u9019\u985e\u60c5\u6cc1\uff0c\u53ef\u4ee5\u63a1\u7528\u4e00\u500b\u660e\u78ba\u7e6b\u7d50\u7684\u8b8a\u9ad4\uff0d\u786c\u7e6b\u7d50\uff0c\u5728\u51fd\u5f0f\u7684\u5167\u90e8\u624b\u52d5\u547c\u53eb <code>call(..)<\/code>\uff0c\u5f37\u5236\u4ee5 obj \u4f5c\u70ba foo \u7684 this \u53c3\u8003\u3002\u5982\u6b64\u4e00\u4f86\uff0c\u4e0d\u8ad6\u4e4b\u5f8c\u5982\u4f55\u8abf\u7528\uff0c\u6700\u7d42\u90fd\u6703\u4ee5 obj \u8abf\u7528 foo\u3002<\/p>\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"js\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"true\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">function foo() {\n\tconsole.log( this.a );\n}\nvar obj = {\n\ta: 2\n};\nvar bar = function() {\n\tfoo.call( obj );\n};\nbar(); \/\/ 2\nsetTimeout( bar, 100 ); \/\/ 2\n\/\/ `bar` hard binds `foo`'s `this` to `obj`\n\/\/ so that it cannot be overriden\nbar.call( window ); \/\/ 2<\/pre>\n\n\n<p>ES5 \u4e2d\u63d0\u4f9b\u4e86 <code>bind(..)<\/code>\uff0c\u56de\u50b3\u4e00\u500b\u65b0\u7684\u51fd\u5f0f\uff0c\u5176\u4e2d\u5beb\u5b9a\u6240\u6307\u5b9a\u7684 this \u60c5\u5883\u7269\u4ef6\u4f86\u547c\u53eb\u51fd\u5f0f\u3002<\/p>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"API_%E5%91%BC%E5%8F%AB%E7%9A%84%E3%80%8C%E6%83%85%E5%A2%83%E3%80%8D\"><\/span>API \u547c\u53eb\u7684\u300c\u60c5\u5883\u300d<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u8a31\u591a\u51fd\u5f0f\u6216\u4e00\u4e9b\u539f\u751f\u5167\u5efa\u51fd\u5f0f\uff0c\u6709\u63d0\u4f9b\u9078\u64c7\u6027\u7684\u53c3\u6578\uff0c\u53ef\u4ee5\u50b3\u905e context \u4f5c\u70ba this \u7684\u53c3\u8003\u3002\u5982 <code>Array.forEach()<\/code>\u3001<code>Array.map()<\/code>\u3002<\/p>\n\n\n<p style=\"background-color:#fbdee6\" class=\"has-background\">\u60f3\u60f3\u9019\u985e\u7684\u4f7f\u7528\u60c5\u5883\uff1f<\/p>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"new_%E7%B9%AB%E7%B5%90\"><\/span><strong>new \u7e6b\u7d50<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u5728 JS \u4e2d\uff0c\u5efa\u69cb\u5668 (constructor) \u53ea\u662f\u524d\u9762\u63a5\u8457 <code>new<\/code> \u904b\u7b97\u5b50\u88ab\u547c\u53eb\u7684\u51fd\u5f0f\uff0c\u800c\u9019\u4f7f\u5f97\u51fd\u5f0f\u547c\u53eb\u8b8a\u6210\u4e86\u4e00\u500b\u5efa\u69cb\u5668\u547c\u53eb\u3002\u5b83\u5011\u53ea\u662f<strong>\u6b63\u898f\u7684\u51fd\u5f0f<\/strong>\uff0c\u4f46\u8abf\u7528\u6642\uff0c\u5176\u884c\u70ba\u5be6\u969b\u4e0a\u6703\u88ab\u524d\u9762\u4f7f\u7528\u7684 <code>new<\/code> \u6240\u63a5\u7ba1\u3002<\/p>\n\n\n<p>\u7576\u51fd\u5f0f\u524d\u9762\u5e36\u6709 <code>new<\/code> \u88ab\u8abf\u7528\u6642\uff0c\u4ee5\u4e0b\u4e8b\u60c5\u6703\u767c\u751f\uff1a<\/p>\n\n\n<ol class=\"wp-block-list\"><li>\u4e00\u500b\u7121\u4e2d\u751f\u6709\u7684\u5168\u65b0\u7269\u4ef6\u88ab\u5efa\u69cb\u51fa\u4f86\u3002<\/li><li>\u65b0\u5efa\u69cb\u7684\u7269\u4ef6\u6703\u5e36\u6709 [[Prototype]] \u9023\u7d50\u3002<\/li><li>\u9019\u500b\u65b0\u5efa\u69cb\u7684\u7269\u4ef6\u6703\u88ab\u8a2d\u70ba\u90a3\u500b\u51fd\u5f0f\u547c\u53eb\u7684 this \u7e6b\u7d50\u3002<\/li><li>\u9664\u975e\u8a72\u51fd\u5f0f\u56de\u50b3\u4e86\u5b83\u81ea\u5df1\u63d0\u4f9b\u7684\u66ff\u4ee3\u7269\u4ef6\uff0c\u4e0d\u7136\u9019\u500b\u51fd\u5f0f\u6703\u81ea\u52d5\u56de\u50b3\u9019\u500b\u65b0\u5efa\u69cb\u7684\u7269\u4ef6\u3002<\/li><\/ol>\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"js\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"true\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">function foo(a) {\n\tthis.a = a;\n}\nvar bar = new foo( 2 );\nconsole.log( bar.a ); \/\/ 2<\/pre>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E4%B8%80%E5%88%87%E9%83%BD%E6%8C%89%E9%A0%86%E5%BA%8F%E4%BE%86\"><\/span><strong>\u4e00\u5207\u90fd\u6309\u9806\u5e8f\u4f86<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u56db\u7a2e\u898f\u5247\u7684\u512a\u5148\u9806\u5e8f\u5982\u4e0b\uff1a<\/p>\n\n\n<ol class=\"wp-block-list\"><li>new \u7e6b\u7d50\uff1a\u8a72\u51fd\u5f0f\u547c\u53eb\u4ee5 <code>new<\/code> \u9032\u884c\u3002<\/li><li>\u660e\u78ba\u7e6b\u7d50\uff1a\u8a72\u51fd\u5f0f\u900f\u904e <code>call(..)<\/code>\u3001<code>apply(..)<\/code>\u3001<code>bind(..)<\/code> \u9032\u884c\u547c\u53eb\u3002<\/li><li>\u96b1\u542b\u7e6b\u7d50\uff1a\u8a72\u51fd\u5f0f\u4ee5\u4e00\u500b\u60c5\u5883 (\u64c1\u6709\u7269\u4ef6\u6216\u5305\u542b\u7269\u4ef6) \u88ab\u547c\u53eb\u3002<\/li><li>\u82e5\u524d\u9762\u898f\u5247\u90fd\u4e0d\u662f\u7528\uff0cthis \u5c31\u662f\u9810\u8a2d\u503c\uff0cglobal \u7269\u4ef6\uff0c\u82e5\u662f\u56b4\u683c\u6a21\u5f0f\u4e2d\u5247\u70ba undefined\u3002<\/li><\/ol>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E7%B9%AB%E7%B5%90%E7%9A%84%E4%BE%8B%E5%A4%96\"><\/span><strong>\u7e6b\u7d50\u7684\u4f8b\u5916<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%BF%BD%E7%95%A5_this\"><\/span>\u5ffd\u7565 this<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u50b3\u5165 null \u6216 undefined \u4f5c\u70ba <code>call(..)<\/code>\u3001<code>apply(..)<\/code>\u3001<code>bind(..)<\/code> \u7684 this \u53c3\u6578\uff0c\u6703\u8f49\u800c\u5957\u7528\u9810\u8a2d\u7e6b\u7d50\u3002<\/p>\n\n\n<p>\u770b\u8d77\u4f86\u5f88\u53cd\u5e38\uff0c\u4f46\u6709\u6642\u6703\u4f7f\u7528 <code>apply(..)<\/code> \u4f86\u6524\u958b\u9663\u5217\u4f5c\u70ba\u51fd\u5f0f\u547c\u53eb\u7684\u53c3\u6578\uff0c\u6216\u662f\u4f7f\u7528 <code>bind(..)<\/code> \u4f86 curry \u53c3\u6578\u3002<\/p>\n\n\n<p>\u4f46\u4f7f\u7528 null \u53ef\u80fd\u6703\u6709\u98a8\u96aa\uff0c\u7279\u5225\u662f\u5728\u4f7f\u7528\u7b2c\u4e09\u65b9\u51fd\u5f0f\u5eab\u7684\u72c0\u6cc1\uff0c\u53ef\u80fd\u6703\u4e0d\u7d93\u610f\u5730\u53c3\u8003\u6216\u4fee\u6539\u5230 global \u7269\u4ef6\u3002\u56e0\u6b64\u5b89\u5168\u7684\u505a\u6cd5\u662f\u50b3\u905e\u4e00\u500b\u7a7a\u7269\u4ef6\uff0c\u4e26\u4e14\u4f7f\u7528\u7279\u6b8a\u7b26\u865f (\u5982 \u00f8 ) \u4f86\u4f5c\u70ba\u8fa8\u8b58\u3002<\/p>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E9%96%93%E6%8E%A5%E5%8F%83%E8%80%83\"><\/span>\u9593\u63a5\u53c3\u8003<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"js\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"true\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">function foo() {\n\tconsole.log( this.a );\n}\nvar a = 2;\nvar o = { a: 3, foo: foo };\nvar p = { a: 4 };\no.foo(); \/\/ 3\n(p.foo = o.foo)(); \/\/ 2<\/pre>\n\n\n<p>\u9593\u63a5\u53c3\u8003\u5be6\u969b\u4e0a\u53ea\u662f\u6307\u5411\u5230\u5e95\u5c64\u7684\u51fd\u5f0f\u7269\u4ef6\uff0c\u6240\u4ee5\u5be6\u969b\u4e0a\u53ea\u662f\u547c\u53eb <code>foo()<\/code>\u3002<\/p>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%BB%9F%E5%8C%96%E7%B9%AB%E7%B5%90\"><\/span>\u8edf\u5316\u7e6b\u7d50<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u53ef\u4ee5\u64b0\u5beb\u4e00\u500b\u8edf\u7e6b\u7d50\u5de5\u5177\uff0c\u70ba\u9810\u8a2d\u7e6b\u7d50\u63d0\u4f9b\u4e00\u500b\u975e global \/ undefined \u7684\u9810\u8a2d\u503c\uff0c\u540c\u6642\u8b93\u51fd\u5f0f\u80fd\u5920\u7d93\u7531\u96b1\u542b\u7e6b\u7d50\u6216\u660e\u78ba\u7e6b\u7d50\u624b\u52d5\u7d66\u5b9a this \u7e6b\u7d50\u3002<\/p>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%AA%9E%E5%BD%99%E7%9A%84_this\"><\/span><strong>\u8a9e\u5f59\u7684 this<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u7bad\u982d\u51fd\u5f0f\u4e0d\u4f7f\u7528\u524d\u9762\u56db\u9805\u898f\u5247\uff0c\u5b83\u7684 this \u7e6b\u7d50\u53d6\u81ea\u5305\u542b\u5b83\u7684\u7bc4\u7587\u3002\u540c\u6642\uff0c\u7bad\u982d\u51fd\u5f0f\u7684\u8a9e\u5f59\u7e6b\u7d50\u7121\u6cd5\u88ab\u8986\u5beb\u3002\u5728 callback \u51fd\u5f0f\u4e2d\u5bb9\u6613\u4f7f\u7528\u5230\u3002<\/p>\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"js\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"true\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">function foo() {\n\tsetTimeout(() =&gt; {\n\t\t\/\/ `this` here is lexically adopted from `foo()`\n\t\tconsole.log( this.a );\n\t},100);\n}\nvar obj = {\n\ta: 2\n};\nfoo.call( obj ); \/\/ 2<\/pre>\n\n\n<p>\u503c\u5f97\u6ce8\u610f\u7684\u662f\uff0c\u7bad\u982d\u51fd\u5f0f\u57fa\u672c\u4e0a\u4f7f\u5f97\u50b3\u7d71\u7684 this \u6a5f\u5236\u6d88\u5931\u4e86\uff0c\u800c\u662f\u63a1\u7528\u8a9e\u5f59\u7bc4\u7587\u3002\u7bad\u982d\u51fd\u5f0f\u96d6\u7136\u770b\u8d77\u4f86\u5438\u5f15\u4eba\uff0c\u4f46\u5b83\u8207 this \u662f\u4e0d\u540c\u98a8\u683c\u548c\u6982\u5ff5\u7684\u7528\u6cd5\uff0c\u8981\u76e1\u53ef\u80fd\u907f\u514d\u6df7\u5408\u4f7f\u7528\u3002<\/p>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%A4%87%E7%BF%92\"><\/span><strong>\u8907\u7fd2<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<ul class=\"wp-block-list\"><li>\u5224\u65b7 this \u7684\u56db\u7a2e\u898f\u5247\u548c\u512a\u5148\u9806\u5e8f\u3002<\/li><li>\u8981\u5c0f\u5fc3\u4e26\u907f\u514d\u89f8\u767c\u9810\u8a2d\u7e6b\u7d50\u898f\u5247\uff0c\u82e5\u8981\u5b89\u5168\u5730\u5ffd\u7565 this \u7e6b\u7d50\uff0c\u53ef\u4ee5\u63a1\u7528\u7a7a\u7269\u4ef6\u4f86\u4f54\u4f4d\uff0c\u6e1b\u5c11\u526f\u4f5c\u7528\u3002<\/li><li>ES6 \u7684\u7bad\u982d\u51fd\u5f0f\u662f\u4f7f\u7528\u8a9e\u5f59\u7bc4\u7587\u4f86\u8655\u7406 this \u7e6b\u7d50\uff0c\u6703\u5f9e\u5305\u542b\u5b83\u5011\u7684\u51fd\u5f0f\u547c\u53eb\u7e7c\u627f this \u7e6b\u7d50\u3002<\/li><\/ul>\n","protected":false},"excerpt":{"rendered":"<p>\u547c\u53eb\u5730\u9ede \u5c0b\u627e\u547c\u53eb\u5730\u9ede\u6642\u9700\u8981\u8003\u616e\u5230\u547c\u53eb\u5806\u758a (ca&hellip;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"pgc_sgb_lightbox_settings":"","footnotes":""},"categories":[13,12],"tags":[21],"class_list":["post-325","post","type-post","status-publish","format-standard","hentry","category-jsclosuresthis","category-12","tag-javascript"],"_links":{"self":[{"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=\/wp\/v2\/posts\/325","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=325"}],"version-history":[{"count":0,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=\/wp\/v2\/posts\/325\/revisions"}],"wp:attachment":[{"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=325"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=325"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=325"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}