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@@ -0,0 +1,72 @@
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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 name="viewport" content="width=device-width, initial-scale=1.0">
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+ <title>Document</title>
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+</head>
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+<body>
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+ <!--
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+ 数据类型:
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+ 六种数据类型
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+
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+ 基本数据类型:
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+ 1,2,3 => Number
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+ '123','4343','' => String
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+ true/false => boolean
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+ a;b;c => undefined
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+ 沒有值 => null (空)
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+
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+ 引用数据类型:
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+ [],{},null => Object
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+
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+
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+
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+ 判断数据类型: typeOf
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+ -->
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+
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+
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+
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+ <script>
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+ // JavaScript 是弱类型语言
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+ // 数据 决定 类型
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+ var a;
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+ // typeof 判断变量的类型
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+ console.log(typeof a);
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+ //undefined 未定义类型:存在 没有赋值
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+ a = 1;
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+ console.log(typeof a,'赋值后');
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+ //number 数字类型
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+ a = '1';
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+ // '' "" 字符串
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+ console.log(typeof a,'新的赋值')
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+ // string 字符串类型
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+ var bbb = true;
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+ console.log(typeof bbb,'bbb')// boolean 布尔值
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+ bbb = false;
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+ console.log(typeof bbb,'新的')// boolean 布尔值:true/false
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+ var ccc = null;
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+ // null 空
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+ console.log(typeof ccc,'ccc') // Object
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+ var ccc = [];
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+ console.log(typeof ccc,'ccc1') // Object
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+ // var ddd = vase;
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+ // [] 数组 {}对象 null => Object对象
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+ console.log(typeof true,'abc')
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+ var news = null;
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+ var sss;
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+ var sss1 = 111;
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+ console.log(typeof news,'news')
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+ console.log(typeof sss,'sss')
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+ console.log(typeof sss1,'sss1')
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+ // null包含undefined
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+ if(null == undefined) {
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+ alert("♥等于")
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+ } else {
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+ alert("♥不等于")
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+ }
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+
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+
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+ </script>
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+</body>
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+</html>
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