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@@ -0,0 +1,49 @@
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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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+ 运算符: + - * / %(取余/取模)
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+ -->
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+ <script>
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+ var a = 1;
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+ var b = 10;
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+ var c = 5;
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+ var d = 21;
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+ // 加法
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+ console.log(a + 3);//4 number + number 加法运算
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+ console.log(a + '90'); //190 number + string 拼接
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+ console.log(a + true); //2 number + boolean 正常运算
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+ console.log(a + undefined);//NaN 非法数字
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+ console.log(a + null);// 1 number+null => number
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+
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+ // 减法
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+ console.log(b - 3);//7 number - number 减法运算
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+ console.log('90' - b); //80 number - string 正常减法运算
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+ console.log(b - true); //9 number - boolean 正常运算
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+ console.log(b - undefined);//NaN 非法数字
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+ console.log(b - null);//10 number-null => number
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+
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+ // 乘法
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+ console.log(c * 3);//15 number * number 乘法运算
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+ console.log('9' * c); //45 number * string 正常运算
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+ console.log(c * true); //5 number * boolean 正常运算
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+ console.log(c * undefined);//NaN 非法数字
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+ console.log(c * null);//0 number*null => 0
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+
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+ // 除法
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+ console.log(d / 3);//7 number * number 除法运算
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+ console.log(d / '3'); //7 number * string 正常运算
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+ console.log(d / false); //Infinity number * boolean 正常运算
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+ console.log(d / undefined);//NaN 非法数字
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+ console.log(d / null);//Infinity number*null => Infinity
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+
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+ // !important > 内联 > id ...
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+ // +infinity 1000 100
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+ </script>
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+</body>
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+</html>
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