{"id":1644,"date":"2022-09-06T09:36:05","date_gmt":"2022-09-06T01:36:05","guid":{"rendered":"https:\/\/zhuxinyong.com\/?p=1644"},"modified":"2022-11-19T23:46:31","modified_gmt":"2022-11-19T15:46:31","slug":"javascript-shi-jue-hua-ti-sheng","status":"publish","type":"post","link":"https:\/\/zhuxinyong.com\/?p=1644","title":{"rendered":"JavaScript \u89c6\u89c9\u5316\uff1a\u63d0\u5347"},"content":{"rendered":"<p><img decoding=\"async\" src=\"https:\/\/zhuxinyong.com\/wp-content\/uploads\/2022\/11\/16624281905738.jpg\" alt=\"\" \/><\/p>\n<p>\u539f\u6587\u5730\u5740\uff1a<a href=\"https:\/\/dev.to\/lydiahallie\/javascript-visualized-hoisting-478h\" target=\"_blank\" rel=\"noopener\">https:\/\/dev.to\/lydiahallie\/javascript-visualized-hoisting-478h<\/a><\/p>\n<p>\u63d0\u5347\u662f\u6bcf\u4e2a JavaScript \u5f00\u53d1\u8005\u542c\u8fc7\u7684\u4f17\u591a\u8bcd\u6c47\u4e2d\u7684\u4e00\u4e2a\uff0c\u56e0\u4e3a\u4f60\u641c\u7d22\u4ee4\u4eba\u607c\u706b\u7684\u95ee\u9898\u65f6\u5230\u6700\u540e StackOverflow \u7684\u4e00\u4e2a\u56de\u7b54\u8005\u544a\u8bc9\u4f60\u90a3\u662f\u56e0\u4e3a<strong>\u63d0\u5347<\/strong>\u5bfc\u81f4\u7684\u3002\u6240\u4ee5\uff0c\u4ec0\u4e48\u662f\u63d0\u5347\uff1f\uff08FYI &#8211; \u4f5c\u7528\u57df\u4f1a\u5728\u53e6\u4e00\u7bc7\u6587\u7ae0\u4e2d\u8bb2\u89e3\uff0c\u6211\u60f3\u4fdd\u6301\u672c\u7bc7\u6587\u7ae0\u77ed\u5c0f\u4e14\u805a\u7126\uff09\u3002<\/p>\n<p>\u5982\u679c\u4f60\u662f JavaScript \u65b0\u624b\uff0c\u53ef\u80fd\u7ecf\u5386\u8fc7\u5947\u602a\u7684\u884c\u4e3a\u3002\u5c31\u662f\u4e00\u4e9b\u53d8\u91cf\u4f1a\u968f\u673a\u7684 <code>undefined<\/code> \u3001 \u629b\u51fa <code>ReferenceErrors<\/code> \u9519\u8bef\u7b49\u7b49\u3002\u63d0\u5347\u7ecf\u5e38\u88ab\u89e3\u91ca\u4e3a\u76f8\u5f53\u4e8e\u628a\u53d8\u91cf\u6216\u51fd\u6570\u79fb\u52a8\u5230\u6587\u4ef6\u5934\u90e8\u3002\u53ef\u5b9e\u9645\u5e76\u4e0d\u662f\u90a3\u6837\uff0c\u5373\u4f7f\u8868\u73b0\u884c\u4e3a\u770b\u7740\u50cf\u3002<\/p>\n<p>\u5f53 JavaScript \u5f15\u64ce\u62ff\u5230\u6211\u4eec\u7684\u811a\u672c\u65f6\uff0c\u7b2c\u4e00\u4ef6\u4e8b\u5c31\u662f\u4e3a\u6211\u4eec\u4ee3\u7801\u4e2d\u7684\u6570\u636e\u5206\u914d\u5185\u5b58\u3002\u6b64\u65f6\u6ca1\u6709\u4ee3\u7801\u6267\u884c\uff0c\u5c31\u4ec5\u4ec5\u662f\u7b80\u5355\u7684\u4e3a\u6267\u884c\u51c6\u5907\u597d\u6240\u6709\u9700\u8981\u7684\u4e1c\u897f\u3002\u51fd\u6570\u58f0\u660e\u548c\u53d8\u91cf\u7684\u5b58\u50a8\u65b9\u5f0f\u662f\u4e0d\u540c\u7684\uff0c\u51fd\u6570\u662f\u4ee5\u5bf9\u6574\u4e2a\u51fd\u6570\u7684\u5f15\u7528\u6765\u5b58\u50a8\u7684\u3002<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/zhuxinyong.com\/wp-content\/uploads\/2022\/11\/gif7.gif\" alt=\"gif7\" \/><\/p>\n<p>\u800c\u53d8\u91cf\uff0c\u6709\u7a0d\u5fae\u7684\u4e0d\u540c\u3002ES6 \u5f15\u5165\u4e86\u4e24\u4e2a\u65b0\u7684\u5173\u952e\u8bcd\u6765\u58f0\u660e\u53d8\u91cf\uff1a<code>let<\/code> \u548c <code>const<\/code>\u3002\u901a\u8fc7 <code>let<\/code> \u548c <code>const<\/code> \u5173\u952e\u8bcd\u58f0\u660e\u7684\u53d8\u91cf\u662f\u672a\u521d\u59cb\u5316\u7684\u3002<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/zhuxinyong.com\/wp-content\/uploads\/2022\/11\/gif8.gif\" alt=\"gif8\" \/><\/p>\n<p>\u901a\u8fc7 <code>var<\/code> \u5173\u952e\u5b57\u58f0\u660e\u7684\u53d8\u91cf\u9ed8\u8ba4\u503c\u4e3a <code>undefined<\/code>\u3002<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/zhuxinyong.com\/wp-content\/uploads\/2022\/11\/gif9.gif\" alt=\"gif9\" \/><\/p>\n<p>\u73b0\u5728\u521b\u5efa\u9636\u6bb5\u5b8c\u6210\uff0c\u6211\u4eec\u53ef\u4ee5\u5b9e\u9645\u6267\u884c\u4ee3\u7801\u4e86\u3002\u5728\u6211\u4eec\u58f0\u660e\u4efb\u4f55\u51fd\u6570\u6216\u53d8\u91cf\u4e4b\u524d\uff0c\u4e00\u8d77\u770b\u770b\u5728\u6587\u4ef6\u5934\u90e8\u82e5\u6709 3 \u4e2a console.log \u8bed\u53e5\u4f1a\u53d1\u751f\u4ec0\u4e48\u3002<\/p>\n<p>\u7531\u4e8e\u51fd\u6570\u58f0\u660e\u662f\u5bf9\u6574\u4e2a\u51fd\u6570\u4ee3\u7801\u7684\u5f15\u7528\uff0c\u6240\u4ee5\u6211\u4eec\u53ef\u4ee5\u5728\u521b\u5efa\u5b83\u4eec\u4e4b\u524d\u8c03\u7528\ud83d\udd25\u3002<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/zhuxinyong.com\/wp-content\/uploads\/2022\/11\/gif16.gif\" alt=\"gif16\" \/><\/p>\n<p>\u5f53\u6211\u4eec\u5728\u5f15\u7528\u4e00\u4e2a\u901a\u8fc7 <code>var<\/code> \u58f0\u660e\u7684\u53d8\u91cf\u4e4b\u524d\u4f7f\u7528\u5b83\u65f6\uff0c\u53ea\u4f1a\u8fd4\u56de\u5b83\u5b58\u50a8\u7684\u9ed8\u8ba4\u503c\uff1a<code>undefined<\/code>\uff01\u53ef\u662f\uff0c\u8fd9\u6709\u65f6\u4f1a\u5bfc\u81f4<code>\u4e0d\u53ef\u9884\u671f\u7684<\/code>\u7684\u884c\u4e3a\u3002\u5728\u591a\u6570\u60c5\u51b5\u4e0b\uff0c\u4ee3\u8868\u4f60\u662f\u65e0\u610f\u5f15\u7528\u5b83\uff08\u4f60\u53ef\u80fd\u5e76\u4e0d\u5e0c\u671b\u5b83\u662f <code>undefined<\/code>\uff09\u3002<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/zhuxinyong.com\/wp-content\/uploads\/2022\/11\/gif17.gif\" alt=\"gif17\" \/><\/p>\n<p>\u4e3a\u4e86\u963b\u6b62\u610f\u5916\u5f15\u7528\u4e00\u4e2a <code>undefined<\/code> \u53d8\u91cf\uff0c\u5c31\u50cf\u4f7f\u7528\u901a\u8fc7 <code>var<\/code> \u5173\u952e\u5b57\u5b9a\u4e49\u7684\u53d8\u91cf\uff0c\u65e0\u8bba\u4f55\u65f6\u6211\u4eec\u4f7f\u7528\u4e00\u4e2a\u672a\u521d\u59cb\u5316\u7684\u53d8\u91cf\u65f6 <code>ReferenceError<\/code> \u9519\u8bef\u5c06\u4f1a\u88ab\u629b\u51fa\u3002\u5728\u5b9e\u9645\u58f0\u660e\u53d8\u91cf\u4e4b\u524d\u7684\u533a\u57df\uff0c\u79f0\u4e3a\uff1a<strong>temporal dead zone<\/strong> \u4f60\u4e0d\u53ef\u4ee5\u5728\u53d8\u91cf\uff08\u4e5f\u5305\u62ec ES6 \u4e2d\u7684 class\uff09\u521d\u59cb\u5316\u4e4b\u524d\u4f7f\u7528\u5b83\u3002<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/zhuxinyong.com\/wp-content\/uploads\/2022\/11\/gif18.gif\" alt=\"gif18\" \/><\/p>\n<p>\u5f53\u6d4f\u89c8\u5668\u5f15\u64ce\u6267\u884c\u8fc7\u6211\u4eec\u5b9e\u9645\u58f0\u660e\u53d8\u91cf\u7684\u4ee3\u7801\u65f6\uff0c\u5185\u5b58\u4e2d\u53d8\u91cf\u7684\u503c\u5c06\u4f1a\u88ab\u6211\u4eec\u58f0\u660e\u5b83\u65f6\u8d4b\u503c\u7684\u503c\u8986\u76d6\u3002<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/zhuxinyong.com\/wp-content\/uploads\/2022\/11\/gif12.gif\" alt=\"gif12\" \/><\/p>\n<p>\u90fd\u7ed3\u675f\u4e86\uff01\u5feb\u901f\u603b\u7ed3\u4e0b\uff1a<\/p>\n<ul>\n<li>\u5f53\u6211\u4eec\u6267\u884c\u4ee3\u7801\u65f6\uff0c\u51fd\u6570\u548c\u53d8\u91cf\u88ab\u5b58\u50a8\u5728\u6267\u884c\u4e0a\u4e0b\u7684\u5185\u5b58\u4e2d\uff0c\u8fd9\u79f0\u4e3a\u63d0\u5347\u3002<\/li>\n<li>\u51fd\u6570\u88ab\u5b58\u50a8\u4e3a\u6307\u5411\u6574\u4e2a\u51fd\u6570\u7684\u4ee3\u7801\u5f15\u7528\u4e2d\uff0c\u901a\u8fc7 <code>var<\/code> \u5173\u952e\u5b57\u58f0\u660e\u7684\u53d8\u91cf\u9ed8\u8ba4\u503c\u4e3a <code>undefined<\/code>\uff0c\u800c <code>let<\/code> \u548c <code>const<\/code> \u5173\u952e\u5b57\u58f0\u660e\u7684\u53d8\u91cf\u5219\u662f\u672a\u521d\u59cb\u5316\u3002<\/li>\n<\/ul>\n<p>\u6211\u5e0c\u671b hosisting \u8fd9\u5757\u77e5\u8bc6\u53d8\u5f97\u6e05\u6670\u4e00\u4e9b\u4e86\uff0c\u7279\u522b\u662f\u5f53\u6211\u4eec\u6267\u884c\u4ee3\u7801\uff0c\u67e5\u627e\u5230\u5e95\u53d1\u751f\u4e86\u4ec0\u4e48\u65f6\u3002\u50cf\u5f80\u5e38\u4e00\u6837\uff0c\u4e0d\u8981\u62c5\u5fc3\u5982\u679c\u5b83\u8fd8\u6ca1\u6709\u5e26\u6765\u5f88\u5b9e\u9645\u7684\u610f\u4e49\u3002\u4f60\u82e5\u7ecf\u5e38\u4f7f\u7528\u5b83\uff0c\u5c31\u4f1a\u8d8a\u6765\u8d8a\u9002\u5e94\u5b83\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u539f\u6587\u5730\u5740\uff1ahttps:\/\/dev.to\/lydiahallie\/javascript-visuali&#46;&#46;&#46;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2,20,3],"tags":[243,242],"class_list":["post-1644","post","type-post","status-publish","format-standard","hentry","category-all","category-frontend","category-tech","tag-hoisting","tag-242"],"_links":{"self":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts\/1644","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1644"}],"version-history":[{"count":1,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts\/1644\/revisions"}],"predecessor-version":[{"id":1645,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=\/wp\/v2\/posts\/1644\/revisions\/1645"}],"wp:attachment":[{"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1644"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1644"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zhuxinyong.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1644"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}