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@@ -0,0 +1,121 @@
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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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+ // 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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+ var c = '333'//string
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+ var d = true //boolean
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+ var f = 'hhahahahah1111'
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+ console.log(f+d)
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+ console.log(c+d) // 字符串拼接
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+ //数据类型里面有 string 进行加法的时候 会变为字符串拼接 */
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+
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+ /* shift + alt + a */
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+ // ctrl + /
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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
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+ console.log(c-d)
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+ var f = 'hahhah111' //string
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+ var e = 1 //Number
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+ console.log(f-e) // NaN */
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+ //当发生减法的时候 字符串内为纯数字 系统会默认把字符串转为数字
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+ //boolean里面 true为1 false 0
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+ // NaN 无法进行计算的结果
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+ //字符串内如果不为纯数字 系统无法计算结果 返回NaN
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+
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+
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+ /* var a = 111; //Number
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+ var b = '3'; //string
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+ console.log(a*b) //进行乘法运算可以转化
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+ var d = false
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+ console.log(a*d) */
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+
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+ /* var a = 111;
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+ var b = true
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+ console.log(a-b) */
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+ //当数字和布尔值进行运算的时候 布尔值都会转化为数字 true = 1 false = 0
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+
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+ /* var a = 123;//number
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+ var b; //undefined
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+ console.log(a+b)//无法进行计算 返回NaN */
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+
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+ /* var a = 111
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+ a++
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+ console.log(a)//112
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+
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+ var b = 222
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+ ++b
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+ console.log(b)//223 */
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+
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+ /* var a = 111;
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+ console.log(a++)//111 先输出 后自增
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+ // a = 112
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+ console.log(++a)//113 先自增 后输出
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+
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+ var h = 666
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+ console.log(--h) //665
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+ console.log(h--)//665
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+ console.log(h)//664 */
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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+'十八'+b)
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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)//true
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+ console.log(a<b)//false
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+ console.log(a=b)//赋值
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+ a = b
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+ console.log(a)
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+ console.log(b)
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+ console.log(a==b)// 判断
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+ //= 进行赋值 == 进行判断 */
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+
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+ // console.log((2<4)==(5>3)==(3<=3)) //true
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+
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+ /* var a = 3
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+ var b = '3'
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+ console.log(a==b)
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+ console.log(a===b) */
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+ /*
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+ = 进行赋值 不进行判断
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+ == 进行判断 但是不判断数据类型
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+ === 进行判断 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 = 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 返回true
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+ != 逻辑非 不等于
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+ */
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+ </script>
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+</body>
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+</html>
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zsydgithub