42 lines
1.5 KiB
HTML
42 lines
1.5 KiB
HTML
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Document</title>
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<script>
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// js 数据类型
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// 基本数据类型 ：number string boolean undefined null
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// 复杂数据类型: object
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// var arr=new Array()
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// var fn=new Function()
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// 基本数据类型和复杂数据类型的区别
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// 检测数据类型
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// 由低到高 typeof instanceof Object.prototype.tostring.call
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// typeof instanceof Object.prototype.toString.call
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var a=9
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var type=Object.prototype.toString.call(a)
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console.log(Object.prototype.toString.call([1,2,3,4]))
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console.log(Object.prototype.toString.call(9),"mmmn")
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console.log(type)
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console.log(9 instanceof Number)
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console.log(new Number(9) instanceof Number)
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console.log([1,2,3,4] instanceof Array)
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console.log(function fn(){} instanceof Function)
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// instanceof 用法 被检测的值 instanceof 猜测的数据类型
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// 返回的是true/false
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var key=123
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console.log(typeof key)
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console.log(typeof null)
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console.log(typeof undefined)
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console.log(typeof [4,3,1])
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console.log(typeof function fm(){})
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</script>
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</head>
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<body>
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</body>
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</html>
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