{"id":257,"date":"2018-12-11T23:59:48","date_gmt":"2018-12-11T15:59:48","guid":{"rendered":"https:\/\/wp.winter-weng.cc\/work\/?p=257"},"modified":"2018-12-11T23:59:48","modified_gmt":"2018-12-11T15:59:48","slug":"ch-2-%e8%aa%9e%e5%bd%99%e7%af%84%e7%96%87","status":"publish","type":"post","link":"https:\/\/wp.winter-weng.cc\/work\/?p=257","title":{"rendered":"Ch. 2 \u8a9e\u5f59\u7bc4\u7587"},"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=257\/#%E8%AA%9E%E5%BD%99%E5%88%86%E6%9E%90%E6%99%82%E6%9C%9F\" >\u8a9e\u5f59\u5206\u6790\u6642\u671f<\/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=257\/#%E6%9F%A5%E6%89%BE\" >\u67e5\u627e<\/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=257\/#%E8%AA%9E%E5%BD%99%E7%AF%84%E7%96%87%E4%BD%9C%E5%BC%8A%E6%8A%80%E5%B7%A7\" >\u8a9e\u5f59\u7bc4\u7587\u4f5c\u5f0a\u6280\u5de7<\/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=257\/#eval\" >eval<\/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=257\/#with\" >with<\/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=257\/#%E6%95%88%E8%83%BD\" >\u6548\u80fd<\/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=257\/#%E8%A4%87%E7%BF%92\" >\u8907\u7fd2<\/a><\/li><\/ul><\/nav><\/div>\n\n<p>\u8a9e\u5f59\u7bc4\u7587\uff1a\u5b9a\u7fa9\u65bc\u7de8\u5beb\u6642\u671f\u3002JS \u63a1\u7528\u6b64\u7a2e\u6a21\u578b\u3002<\/p>\n\n\n<p>\u52d5\u614b\u7bc4\u7587\uff1a\u4e0d\u5728\u610f\u5ba3\u544a\uff0c\u800c\u53d6\u6c7a\u65bc\u5f9e\u4f55\u8655\u88ab\u547c\u53eb\u3002(\u9644\u9304 A)<\/p>\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"true\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">function foo() {\n\tconsole.log(a); \/\/ \u8a9e\u5f59\u7bc4\u7587\uff1a\u5370\u51fa 2\uff1b\u52d5\u614b\u7bc4\u7587\uff1a\u5370\u51fa 3\u3002\n}\nfunction bar() {\n\tvar a = 3;\n\tfoo();\n}\nvar a = 2;\nbar();\n<\/pre>\n\n\n<hr class=\"wp-block-separator\" \/>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E8%AA%9E%E5%BD%99%E5%88%86%E6%9E%90%E6%99%82%E6%9C%9F\"><\/span><strong>\u8a9e\u5f59\u5206\u6790\u6642\u671f<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>\u8a9e\u5f59\u7bc4\u7587\u662f\u5728\u8a9e\u5f59\u5206\u6790\u6642\u671f (lexing) \u5b9a\u7fa9\u7684\u7bc4\u7587\u3002\u8996\u8b8a\u6578\u8207\u5340\u584a\u5728\u5beb\u4f5c\u6642\u671f\u88ab\u653e\u7f6e\u65bc\u4f55\u8655\u4f86\u6c7a\u5b9a\u3002\u8a9e\u5f59\u5206\u6790\u6642\u671f\u80fd\u77e5\u9053\u6240\u6709\u8b58\u5225\u5b57\u65bc\u4f55\u8655\u5ba3\u544a\uff0c\u4ee5\u9810\u6e2c\u57f7\u884c\u904e\u7a0b\u4e2d\u6703\u5982\u4f55\u88ab\u67e5\u627e\u3002<\/p>\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"https:\/\/github.com\/getify\/You-Dont-Know-JS\/raw\/master\/scope%20%26%20closures\/fig2.png\" alt=\"\" \/><\/figure>\n\n\n<ol class=\"wp-block-list\"><li>Bubble 1\uff1afoo<\/li><li>Bubble 2\uff1aa, bar, b<\/li><li>Bubble 3\uff1ac<\/li><\/ol>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E6%9F%A5%E6%89%BE\"><\/span>\u67e5\u627e<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<ul class=\"wp-block-list\"><li>\u906e\u853d\uff1a\u76f8\u540c\u8b58\u5225\u5b57\u53ef\u80fd\u51fa\u73fe\u5728\u4e0d\u540c\u7684\u7bc4\u7587\u4e2d\uff0c\u4f46\u53ea\u8981\u627e\u5230\u7b2c\u4e00\u500b\u5c31\u6703\u505c\u6b62\u52d5\u4f5c\u3002\u610f\u5373\uff0c\u5167\u5c64\u7684\u8b58\u5225\u5b57\u6703\u906e\u853d\u5176\u4ed6\u5916\u5c64\u8b58\u5225\u5b57\u3002<\/li><li>\u5168\u57df\u8b8a\u6578\uff1a\u5168\u57df\u8b8a\u6578\u6703\u81ea\u52d5\u6210\u70ba\u5168\u57df\u7269\u4ef6\u7684\u5c6c\u6027 (e.g. <code>window.a<\/code>)\uff0c\u56e0\u6b64\u53ef\u4ee5\u62ff\u4f86\u907f\u514d\u8b8a\u6578\u88ab\u906e\u853d\u800c\u53d6\u4e0d\u5230\u7684\u554f\u984c\u3002<\/li><\/ul>\n\n\n<p>\u67e5\u627e\u52d5\u4f5c\u6c38\u9060\u5f9e\u7576\u6642\u57f7\u884c\u7684\u7bc4\u7587\u958b\u59cb\uff0c\u4e26\u5f80\u5916\u6216\u5f80\u4e0a\u5c0b\u627e\uff0c\u76f4\u5230\u627e\u5230\u7b2c\u4e00\u500b\u7b26\u5408\u7684\u70ba\u6b62\u3002<\/p>\n\n\n<p>\u67e5\u627e\u52d5\u4f5c\u53ea\u9069\u7528\u65bc\u4e00\u7d1a\u8b58\u5225\u5b57\uff0c\u5982 <code>foo.bar.baz<\/code>\uff0c\u53ea\u6703\u67e5\u627e foo\u3002\u5f8c\u7e8c\u4ea4\u7531\u7269\u4ef6\u5c6c\u6027\u5b58\u53d6\u898f\u5247\u7e7c\u7e8c\u89e3\u6790\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%AA%9E%E5%BD%99%E7%AF%84%E7%96%87%E4%BD%9C%E5%BC%8A%E6%8A%80%E5%B7%A7\"><\/span><strong>\u8a9e\u5f59\u7bc4\u7587\u4f5c\u5f0a\u6280\u5de7<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"eval\"><\/span>eval<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>eval \u53ef\u4ee5\u50b3\u5165\u4e00\u500b\u5b57\u4e32\u4f5c\u70ba\u53c3\u6578\uff0c\u4e26\u5c07\u8a72\u5b57\u4e32\u5167\u5bb9\u8996\u70ba\u7a0b\u5f0f\u539f\u672c\u5df2\u7d93\u7de8\u5beb\u597d\u7684\u7a0b\u5f0f\u78bc\u3002<\/p>\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"true\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">function foo(str, a) {\n\teval(str); \/\/ var b = 3;\n\tconsole.log(a, b);\n}\nvar b = 2;\nfoo('var b = 3;', 1); \/\/ 1 3\n<\/pre>\n\n\n<p><code>var b = 3;<\/code> \u88ab\u8996\u70ba\u4e00\u76f4\u90fd\u5728\u90a3\u88cf\u7684\u7a0b\u5f0f\u78bc\uff0cb \u56e0\u6b64\u906e\u853d\u4e86\u5916\u5c64\u5168\u57df\u7684 b\u3002<\/p>\n\n\n<p class=\"has-text-color has-vivid-red-color\">eval \u80fd\u5728\u57f7\u884c\u6642\u671f\u4fee\u6539\u7de8\u5beb\u6642\u671f\u7684\u8a9e\u5f59\u7bc4\u7587\u3002<\/p>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"with\"><\/span>with<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>with \u63a5\u53d7\u4e00\u500b\u7269\u4ef6\uff0c\u4e26\u628a\u7269\u4ef6\u4f5c\u70ba\u7368\u7acb\u7684\u8a9e\u5f59\u7bc4\u7587\u770b\u5f85\uff0c\u5c07\u7269\u4ef6\u5c6c\u6027\u8996\u70ba\u8a72\u7bc4\u7587\u4e0b\u7684\u8b58\u5225\u5b57\u3002<\/p>\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"true\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">function foo(obj) {\n\twith (obj) {\n\t\ta = 2;\n\t}\n}\nvar o2 = {\n\tb: 3\n};\nfoo(o2);\nconsole.log(o2.a); \/\/ undefined\nconsole.log(a); \/\/ 2\uff0c\u5168\u57df\u503c\u5916\u6f0f\n<\/pre>\n\n\n<p>\u8003\u616e\u4ee5\u4e0a\u7a0b\u5f0f\u78bc\uff0c\u7576\u5728\u7bc4\u7587\u4e2d\u627e\u4e0d\u5230 a \u6642\uff0cLHS \u67e5\u627e\u5f8c\u81ea\u52d5\u7522\u751f\u5168\u57df\u8b8a\u6578 a\u3002<\/p>\n\n\n<p class=\"has-text-color has-vivid-red-color\">with \u80fd\u5728\u57f7\u884c\u6642\u671f\u5c07\u7269\u4ef6\u505a\u70ba\u4e00\u500b\u7bc4\u7587\u4f86\u770b\u5f85\u3002<\/p>\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"%E6%95%88%E8%83%BD\"><\/span>\u6548\u80fd<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<p>eval \u548c with \u5169\u8005\u5728\u57f7\u884c\u6642\u671f\u4fee\u6539\u4e86\u7de8\u5beb\u6642\u671f\u7684\u8a9e\u5f59\u7bc4\u7587\uff1b\u6216\u662f\u5efa\u7acb\u4e86\u65b0\u7684\u8a9e\u5f59\u7bc4\u7587\u3002<\/p>\n\n\n<p>Engine \u5728\u7de8\u8b6f\u6642\u671f\u6703\u9032\u884c\u6700\u4f73\u5316\uff0c\u4e8b\u5148\u78ba\u5b9a\u6240\u6709\u8b8a\u6578\u548c\u5ba3\u544a\u7684\u4f4d\u7f6e\u3002\u7136\u800c\u82e5\u5b83\u767c\u73fe\u4e86 eval \u548c with\uff0c\u4ee3\u8868\u5b83\u539f\u5148\u505a\u7684\u975c\u614b\u5206\u6790\u53ef\u80fd\u90fd\u662f\u7121\u6548\u7684\uff0c\u65bc\u662f\u5b83\u4e7e\u8106\u653e\u68c4\u4e86\u6700\u4f73\u5316\uff0c\u5c0e\u81f4\u6548\u80fd\u4e0b\u964d\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>\u8acb\u8aaa\u660e\u8a9e\u5f59\u7bc4\u7587\u3002<\/li><li>eval \u8207 with \u7684\u7f3a\u9ede\u3002<\/li><\/ul>\n","protected":false},"excerpt":{"rendered":"<p>\u8a9e\u5f59\u7bc4\u7587\uff1a\u5b9a\u7fa9\u65bc\u7de8\u5beb\u6642\u671f\u3002JS \u63a1\u7528\u6b64\u7a2e\u6a21\u578b\u3002 \u52d5&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-257","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\/257","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=257"}],"version-history":[{"count":0,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=\/wp\/v2\/posts\/257\/revisions"}],"wp:attachment":[{"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=257"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=257"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wp.winter-weng.cc\/work\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=257"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}