{"id":3217,"date":"2019-06-24T19:06:39","date_gmt":"2019-06-24T11:06:39","guid":{"rendered":"http:\/\/www.daliane.com\/?p=3217"},"modified":"2019-06-24T19:06:43","modified_gmt":"2019-06-24T11:06:43","slug":"javascript_qi_zhong_shu_ju_lei_xing","status":"publish","type":"post","link":"http:\/\/www.daliane.com\/category\/jinjiaoyou\/javascript_qi_zhong_shu_ju_lei_xing\/","title":{"rendered":"JavaScript \u4e03\u79cd\u6570\u636e\u7c7b\u578b"},"content":{"rendered":"
\n

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\n\t<\/h3>\n<\/div>\n
\n

\n\t\t1\u3001\u5185\u7f6e\u7c7b\u578b
\n\t<\/h3>\n<\/div>\n
\n

\n\t\tJavaScript\u6709\u4e03\u79cd\u5185\u7f6e\u7c7b\u578b:
\n\"\u56fe\u7247\u63cf\u8ff0\"\n\t<\/p>\n<\/div>\n

\n

\n\t\t2\u3001\u7c7b\u578b\u68c0\u6d4b typeof
\n\t<\/h3>\n<\/div>\n
\n
1 typeof undefined === 'undefined';\/\/true\r\n2 typeof 'abc' === 'string';\/\/true\r\n3 typeof 123 === 'number';\/\/true\r\n4 typeof true === 'boolean';\/\/true\r\n5 typeof {a:'test'} === 'object';\/\/true\r\n6 typeof Symbol() === 'symbol';\/\/true<\/pre>\n<\/div>\n
\n
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typeof null === 'object';\/\/true<\/pre>\n<\/div>\n
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var a = null;\r\n if(!a&&typeof a === 'object'){\r\n     \/\/\u6b64\u523b\u8bf4\u660ea\u7684\u503c\u662fnull\r\n     \r\n }<\/pre>\n<\/div>\n
\n
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typeof function a(){} === 'function';\/\/true\r\ntypeof [1,2,3] === 'object';\/\/object<\/pre>\n<\/div>\n
\n
\n
\n\t\t\t\u51fd\u6570\u548c\u6570\u7ec4\u90fd\u662f\u5bf9\u8c61\u7684\u5185\u7f6e\u7c7b\u578b\uff0c\u7b97\u662fobject\u7684\u2018\u5b50\u7c7b\u578b\u2019\u3002
\n\u51fd\u6570\u53ef\u4ee5\u62e5\u6709\u5c5e\u6027\uff0c\u4f8b\u5982a.length;\/\/0;\n\t\t<\/p>\n<\/blockquote>\n<\/div>\n
\n
\n\t\t2\u3001\u503c\u548c\u7c7b\u578b
\n\t<\/h3>\n<\/div>\n
\n
\n
\n\t\t\tJavaScritp\u4e2d\u7684\u53d8\u91cf\u662f\u6ca1\u6709\u7c7b\u578b\u7684\uff0c\u53ea\u6709\u503c\u624d\u6709\u3002\u53d8\u91cf\u53ef\u4ee5\u968f\u65f6\u6301\u6709\u4efb\u4f55\u7c7b\u578b\u7684\u503c
\n\u8bed\u8a00\u5f15\u64ce\u4e0d\u8981\u6c42\u53d8\u91cf\u603b\u662f\u6301\u6709\u4e0e\u5176\u521d\u59cb\u503c\u540c\u7c7b\u578b\u7684\u503c\u3002\u4e00\u4e2a\u53d8\u91cf\u53ef\u4ee5\u5148\u88ab\u8d4b\u503c\u4e3a\u5b57\u7b26\u4e32\u540e\u91cd\u65b0\u8d4b\u503c\u4e3a\u6570\u5b57\uff0c\u4e0d\u4f1a\u62a5\u9519\u3002\n\t\t<\/p>\n<\/blockquote>\n<\/div>\n
\n
\n\t\t3\u3001undefined\u548cundeclared
\n\t<\/h3>\n<\/div>\n
\n
\n
\n\t\t\t\u53d8\u91cf\u5728\u672a\u6301\u6709\u503c\u7684\u65f6\u5019\u4e3aundefined\uff0c\u6b64\u65f6typeof \u8fd4\u56de \u2019 undefined ‘;
\n\u5df2\u5728\u4f5c\u7528\u57df\u4e2d\u58f0\u660e\u4f46\u6ca1\u6709\u8d4b\u503c\u7684\u53d8\u91cf\u8fd4\u56de\u503c\u662fundefined\uff0c\u5728\u4f5c\u7528\u57df\u4e2d\u6ca1\u58f0\u660e\u8fc7\u7684\u53d8\u91cf\u8fd4\u56de\u503c\u662f\uff1aReferenceError: \u53d8\u91cf\u540d is not defined\n\t\t<\/p>\n<\/blockquote>\n<\/div>\n
\n
var a ;\r\n a;\/\/undefined\r\n b;\/\/ReferenceError : b is not defined<\/pre>\n<\/div>\n
\n
\n
\n\t\t\t\u8fd9\u91cc\u6709\u4e00\u4e2a\u8981\u6ce8\u610f\u7684\u70b9\uff1atypeof \u5bf9\u4e8e\u672a\u58f0\u660e\u8fc7\u548c\u58f0\u660e\u8fc7\u672a\u8d4b\u503c\u7684\u53d8\u91cf\u8fd4\u56de\u7ed3\u679c\u90fd\u662f\u2018undefined\u2019\n\t\t<\/p>\n<\/blockquote>\n<\/div>\n
\n
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\n\t<\/h3>\n<\/div>\n
\n
if(typeof myTest !== 'undefined'){\r\n    console.log('myTest\u5df2\u7ecf\u5b58\u5728')\r\n}\r\nif(typeof atob === 'undefined'){\r\n    atob = function(){}\r\n}<\/pre>\n<\/div>\n
\n
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\n
function doSomethingCool(FeatureXyz){\r\n    var helper = FeatureXyz || function(){}\r\n    var val = helper();\r\n}<\/pre>\n<\/div>\n
\n
\n\t\t5\u3001\u603b\u7ed3\uff1a
\n\t<\/h3>\n<\/div>\n
\n
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