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@@ -0,0 +1,112 @@
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+<!DOCTYPE html>
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+<html lang="en">
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+
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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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+
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+<body>
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+ <script>
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+ // var a = 111
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+ // var b = 222
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+ // console.log(a+b)
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+ // console.log(a-b)
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+ // console.log(a*b)
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+
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+ /* var a = 111 //number
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+ var b = '222' //string
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+ console.log(a+b) //字符串拼接 number + string
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+
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+ var c = true //boolean
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+ console.log(b+c)
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+ //数据里面 有string类型 相加进行字符串拼接 */
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+
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+ /* var a = 111 //number
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+ var b = '222' //string
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+ console.log(b-a)
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+ var c = '333'
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+ var d = true //boolean
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+ console.log(c-d)
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+ var f = 'hahahahahahahaxixixi1111'
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+ console.log(f-a) //NaN
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+ //当发生减法的时候 string里面是否是纯数字 如果是纯数字 那么就会转化为number类型 参与计算
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+ //如果不是纯数字 无法参与运算 结果NaN
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+ //boolean 里面的值 true = 1 false = 0 参与运算 */
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+
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+
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+ /* var a = 111
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+ var b = undefined
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+ console.log(a + b)
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+ //与undefined参加运算 无法运算 结果为NaN */
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+
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+ /* var a = 111
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+ var b = '3'
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+ console.log(a*b)
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+ var c = false
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+ console.log(a*c) */
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+
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+
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+ /* var a = '我叫'
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+ var b = '小明'
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+ console.log(a + b) */
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+
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+ // var a = 111
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+ // a--
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+ // console.log(a)
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+
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+
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+ // var a = 111
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+ // ++a
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+ // console.log(a)
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+
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+ /* var a = 111
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+ console.log(a++)//先输出 后自增 最后变为 112
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+ console.log(++a)//先自增 后输出 最后变为113
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+ var h = 666
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+ console.log(--h)
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+ console.log(h--)
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+ console.log(h) */
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+
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+
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+ // var a = '今天'
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+ // var b = '摄氏度'
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+ // console.log(a + '零下20' + b)
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+
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+
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+ // var a = '18岁'
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+ // alert('我的年龄' + a)
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+
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+ // var a = 5
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+ // var b = 4
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+ // console.log(a > b)
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+ // console.log(a < b)
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+ // console.log(a = b)
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+
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+ // = 代表赋值
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+ // == 代表判断 不判断数据类型
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+ // === 代表判断 同时判断数据类型
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+
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+ // var a = 5
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+ // var b = '5'
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+ // console.log(a === b)
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+ // console.log((2 < 4) == (5 > 3) == (3 <= 3)) //true
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+
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+
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+ var a = 5
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+ var b = 4
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+ console.log(a > 5 && b < 6)
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+ console.log(a > 4 || b < 4)
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+ console.log(a != 4)
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+
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+ /*
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+ && 逻辑与 当两边都为true 才返回true
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+ || 逻辑或 当一边为true 就返回true
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+ ! 逻辑非
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+ */
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+ </script>
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+</body>
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+
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+</html>
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zsydgithub