{"id":265,"date":"2018-12-17T23:02:20","date_gmt":"2018-12-17T15:02:20","guid":{"rendered":"https:\/\/wp.winter-weng.cc\/work\/?p=265"},"modified":"2018-12-17T23:02:20","modified_gmt":"2018-12-17T15:02:20","slug":"ch-4-%e6%8b%89%e5%8d%87","status":"publish","type":"post","link":"https:\/\/wp.winter-weng.cc\/work\/?p=265","title":{"rendered":"Ch. 4 \u62c9\u5347"},"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=265\/#%E7%B7%A8%E8%AD%AF%E5%99%A8%E5%86%8D%E6%AC%A1%E5%87%BA%E6%93%8A\" >\u7de8\u8b6f\u5668\u518d\u6b21\u51fa\u64ca<\/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=265\/#%E5%87%BD%E5%BC%8F%E5%84%AA%E5%85%88\" >\u51fd\u5f0f\u512a\u5148<\/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=265\/#%E8%A4%87%E7%BF%92\" >\u8907\u7fd2<\/a><\/li><\/ul><\/nav><\/div>\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=\"\">a = 2;\nvar a;\nconsole.log(a);\n\/* reality --------------------------------- *\/\nvar a; \/\/ hoisting\na = 2;\nconsole.log(a); \/\/ 2<\/pre>\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=\"\">console.log(a); \/\/ undefined\nvar a = 2;\n\/* reality --------------------------------- *\/\nvar a; \/\/ hoisting\nconsole.log(a); \/\/ undefined\na = 2;<\/pre>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E7%B7%A8%E8%AD%AF%E5%99%A8%E5%86%8D%E6%AC%A1%E5%87%BA%E6%93%8A\"><\/span><strong>\u7de8\u8b6f\u5668\u518d\u6b21\u51fa\u64ca<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<ul class=\"wp-block-list\"><li>\u8b8a\u6578\u8207\u51fd\u5f0f\u5ba3\u544a\u88ab\u79fb\u52d5\u5230\u7a0b\u5f0f\u78bc\u9802\u7aef \u21d2 \u62c9\u5347\u3002<\/li><li>\u53ef\u57f7\u884c\u908f\u8f2f\u8207\u6307\u6d3e\u6703\u7559\u5728\u539f\u8655\u3002\u51fd\u5f0f\u904b\u7b97\u5f0f\u4e5f\u662f\u3002<\/li><li>\u62c9\u5347\u52d5\u4f5c\u662f\u9010\u500b\u7bc4\u7587 (per-scope) \u9032\u884c\u7684\u3002<\/li><li>\u51fd\u5f0f\u904b\u7b97\u5f0f\u7684\u60c5\u6cc1\uff1a<\/li><\/ul>\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=\"\">foo();\nbar();\nvar foo = function bar() {\n\t...\n}\n\/* reality --------------------------------- *\/\nvar foo;\nfoo(); \/\/ typeError\nbar(); \/\/ referenceError\nfoo = function() {\n\tvar bar = ...self...\n}<\/pre>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E5%87%BD%E5%BC%8F%E5%84%AA%E5%85%88\"><\/span><strong>\u51fd\u5f0f\u512a\u5148<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<ul class=\"wp-block-list\"><li>\u51fd\u5f0f\u5ba3\u544a\u8207\u8b8a\u6578\u90fd\u6703\u88ab\u62c9\u5347\uff0c\u4f46\u51fd\u5f0f\u512a\u5148\u65bc\u8b8a\u6578\u3002<\/li><li>\u5f8c\u7e8c\u7684\u51fd\u5f0f\u5ba3\u544a\u6703\u8986\u84cb\u524d\u9762\u7684\u51fd\u5f0f\u3002<\/li><\/ul>\n\n\n<p style=\"background-color:#fbdee6\" class=\"has-background\">P.52 \u51fa\u73fe\u5728\u6b63\u5e38\u5340\u584a\u5167\u7684\u51fd\u5f0f\u5ba3\u544a\u901a\u5e38\u6703\u88ab\u62c9\u5347\u5230\u5305\u542b\u5b83\u7684\u7bc4\u7587\uff0c\u800c\u975e\u50cf\u9019\u6bb5\u7a0b\u5f0f\u78bc\u6697\u793a\u7684\u90a3\u6a23\u662f\u689d\u4ef6\u5f0f\u3002\u21d2 \u770b\u4e0d\u592a\u61c2 ^^|||<\/p>\n\n\n<p style=\"background-color:#fff8e3\" class=\"has-background\">P.52 \u7a0b\u5f0f\u78bc\uff1a\u61c9\u8a72\u8981\u5169\u500b foo() \u90fd\u88ab\u62c9\u5347\uff0c\u4e26\u4e14\u5f8c\u9762\u84cb\u6389\u524d\u9762\uff0c\u800c\u5370\u51fa b\u3002\u4f46\u5728 Chrome \u4e0a\uff0c\u6703\u4e00\u958b\u59cb\u5c31\u51fa\u73fe TypeError\u3002if .. else .. \u7684 { } \u61c9\u8a72\u53ea\u662f\u98a8\u683c\uff0c\u800c\u4e0d\u5177\u6709\u5340\u584a\u7bc4\u7587\u7684\u7279\u6027\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><code>var a = 2;<\/code> \u5be6\u969b\u4e0a\u662f\u5169\u500b\u8ff0\u53e5\u3002<\/li><li>\u8aaa\u660e\u62c9\u5347 (hoisting)\u3002<\/li><\/ul>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<p>\u5ef6\u4f38\u95b1\u8b80\uff1a<a href=\"https:\/\/blog.techbridge.cc\/2018\/11\/10\/javascript-hoisting\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"\u5ef6\u4f38\u95b1\u8b80\uff1a\u6211\u77e5\u9053\u4f60\u61c2 hoisting\uff0c\u53ef\u662f\u4f60\u4e86\u89e3\u5230\u591a\u6df1\uff1f (opens in a new tab)\">\u6211\u77e5\u9053\u4f60\u61c2 hoisting\uff0c\u53ef\u662f\u4f60\u4e86\u89e3\u5230\u591a\u6df1\uff1f<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u7de8\u8b6f\u5668\u518d\u6b21\u51fa\u64ca \u8b8a\u6578\u8207\u51fd\u5f0f\u5ba3\u544a\u88ab\u79fb\u52d5\u5230\u7a0b\u5f0f\u78bc\u9802\u7aef &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-265","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\/265","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=265"}],"version-history":[{"count":0,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=\/wp\/v2\/posts\/265\/revisions"}],"wp:attachment":[{"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=265"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=265"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=265"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}