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@@ -0,0 +1,75 @@
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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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+</head>
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+<body>
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+ <script>
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+ /*
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+ const 和 var的区别
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+ 1.const 不能重复赋值
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+ 2.const 不能重复声明
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+ 3.const 没有变量提升
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+ 4.const 具有块级作用域
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+ 5.const 临时失效区
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+ */
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+ // const a = 100
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+ // a = 200
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+ // console.log(a)
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+
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+
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+ // const a = 100
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+ // const a = 200
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+ // console.log(a)
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+
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+ // console.log(a)
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+ // const a = 100
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+
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+ // const a = 100
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+ // function fn(){
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+ // a = 10
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+ // console.log(a)
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+ // }
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+ // fn()
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+
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+ // var a = true
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+ // if(a){
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+ // const x = 100
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+ // }
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+ // console.log(x)
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+
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+
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+
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+
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+ var a = true
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+ if(a){
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+ var b = 10
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+ let x = 100
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+ }
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+ b = 30
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+ x = 10
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+ const c = 200
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+ function fn(){
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+ console.log(b)
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+ // console.log(h)
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+ // console.log(xx)
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+ let xx = 30
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+ var b = 300
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+ const x = 30
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+ console.log(x)
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+ console.log(c)
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+ }
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+ fn()
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+ console.log(a,b,x,c)
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+
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+ // undefined 报错 30 200 true,30,报错,200
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+ // undefined 报错 10 200 true,30,报错,200
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+ // undefined 报错 30 200 true,30,10,200
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+ // undefined 报错 30 200 true,300,报错,200
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+
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+ </script>
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+</body>
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+</html>
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zsydgithub