【JavaScript笔记】JavaScript基础_运算符(2)
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这里整理了常用的运算符，在代码的注释里一起描述了运算符的含义。
1.加法(+)
<!DOCType html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript">
console.log("--------------------加法--------------------");
var aa = 12 + 1;
console.log("aa type:", typeof aa); //aa type: number
console.log("aa:", aa); //aa: 13
aa = 12 + true;
console.log("aa type:", typeof aa); //aa type: number
console.log("aa:", aa); //aa: 13
aa = true + false;
console.log("aa type:", typeof aa); //aa type: number
console.log("aa:", aa); //aa: 1
aa = 12 + null;
console.log("aa type:", typeof aa); //aa type: number
console.log("aa:", aa); //aa: 12
aa = 12 + NaN;
console.log("aa type:", typeof aa); //aa type: number
console.log("aa:", aa); //aa: NaN
aa = 12 + undefined;
console.log("aa type:", typeof aa); //aa type: number
console.log("aa:", aa); //aa: NaN
aa = "你好" + "世界"; //加法中只要有字符串，会先转字符串后在做加法
console.log("aa type:", typeof aa); //aa type: string
console.log("aa:", aa); //aa: 你好世界
aa = 1 + 2 + "3";
console.log("aa type:", typeof aa); //aa type: string
console.log("aa:", aa); //aa: 33
aa = 1 + "2" + 3;
console.log("aa type:", typeof aa); //aa type: string
console.log("aa:", aa); //aa: 123
aa = true + "你好";
console.log("aa type:", typeof aa); //aa type: string
console.log("aa:", aa); //aa: true你好
aa = 12 + "";
console.log("aa type:", typeof aa); //aa type: string
console.log("aa:", aa); //aa: 12
aa = null + "";
console.log("aa type:", typeof aa); //aa type: string
console.log("aa:", aa); //aa: null
aa = "12";
aa = +aa;
console.log("aa type:", typeof aa); //aa type: number
console.log("aa:", aa); //aa: 12
aa = 1 + +"2" + 3;
console.log("aa type:", typeof aa); //aa type: number
console.log("aa:", aa); //aa: 6
</script>
</head>
<body>
</body>
</html>
2.减法(-)
<!DOCType html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript">
console.log("--------------------减法--------------------");
var bb = 12 - 1;
console.log("bb type:", typeof bb); //bb type: number
console.log("bb:", bb); //bb: 11
bb = 12 - "1";
console.log("bb type:", typeof bb); //bb type: number
console.log("bb:", bb); //bb: 11
bb = 12 - true;
console.log("bb type:", typeof bb); //bb type: number
console.log("bb:", bb); //bb: 11
bb = 12 - NaN;
console.log("bb type:", typeof bb); //bb type: number
console.log("bb:", bb); //bb: NaN
bb = 12 - null;
console.log("bb type:", typeof bb); //bb type: number
console.log("bb:", bb); //bb: 12
bb = 12 - undefined;
console.log("bb type:", typeof bb); //bb type: number
console.log("bb:", bb); //bb: NaN
aa = "12";
aa = -aa;
console.log("aa type:", typeof aa); //aa type: number
console.log("aa:", aa); //aa: -12
</script>
</head>
<body>
</body>
</html>
3.乘法(*),除法(/),取模(%)
<!DOCType html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript">
console.log("--------------------乘法(*),除法(/),取模(%)--------------------");
var cc = 12 * 2;
console.log("cc type:", typeof cc); //cc type: number
console.log("cc:", cc); //cc: 24
cc = 12 * "2";
console.log("cc type:", typeof cc); //cc type: number
console.log("cc:", cc); //cc: 24
cc = 12 * null;
console.log("cc type:", typeof cc); //cc type: number
console.log("cc:", cc); //cc: 0
cc = 12 * NaN;
console.log("cc type:", typeof cc); //cc type: number
console.log("cc:", cc); //cc: NaN
cc = 12 * undefined;
console.log("cc type:", typeof cc); //cc type: number
console.log("cc:", cc); //cc: NaN
cc = 12 / "2";
console.log("cc type:", typeof cc); //cc type: number
console.log("cc:", cc); //cc: 6
cc = 12 % "5";
console.log("cc type:", typeof cc); //cc type: number
console.log("cc:", cc); //cc: 2
</script>
</head>
<body>
</body>
</html>
4. ++ 和 –
<!DOCType html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript">
console.log("--------------------【 ++ 和 -- 】--------------------");
var cc = 1;
console.log(cc++); // 1
console.log("cc:", cc); //cc: 2
cc = 1;
console.log(++cc); // 2
console.log("cc:", cc); //cc: 2
cc = 2;
console.log(--cc); // 1
console.log("cc:", cc); //cc: 2
cc = 1;
// 1 + 3 + 3
cc= cc++ + ++cc + cc;
console.log("cc:", cc); //cc: 7
console.log("--------------------【 += -= *= /= %= 】--------------------");
//和其他语言一样，这里就不做整理了。
</script>
</head>
<body>
</body>
</html>
5. ! && ||
<!DOCType html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript">
console.log("--------------------【 ! && || 】--------------------");
// ! 取反 && 与 || 或
var dd = "true";
dd = !!dd;
console.log("dd type:", typeof dd); //dd type: boolean
console.log("dd:", dd); // dd: true
dd = !dd;
console.log("dd type:", typeof dd); //dd type: boolean
console.log("dd:", dd); // dd: false
//如果两个都是true,返回后面的
dd = 5 && 6;
console.log("dd type:", typeof dd); //dd type: boolean
console.log("dd:", dd); // dd: 6
//如果有一个是false,返回前面的值
dd = 0 && 6;
console.log("dd type:", typeof dd); //dd type: boolean
console.log("dd:", dd); // dd: 0
dd = NaN && 0;
console.log("dd type:", typeof dd); //dd type: boolean
console.log("dd:", dd); // dd: NaN
//返回靠前的true, 都是false返回后面的false
dd = 2 || 1;
console.log("dd type:", typeof dd); //dd type: boolean
console.log("dd:", dd); // dd: 2
dd = 0 || 2;
console.log("dd type:", typeof dd); //dd type: boolean
console.log("dd:", dd); // dd: 2
dd = NaN || 0;
console.log("dd type:", typeof dd); //dd type: boolean
console.log("dd:", dd); // dd: 0
</script>
</head>
<body>
</body>
</html>
6. 比较预算符(> >= < <= != == !== ===)
<!DOCType html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript">
console.log("--------------------【 > >= < <= 】--------------------");
console.log(5 > 6); //false
console.log(5 <= 6); //true
console.log(1 >= true); //true
console.log(10 >= null); //true
//任何值和NaN比较都是false
console.log(10 >= "Hi"); //false
console.log(10 <= "Hi"); //false
console.log("7" > "5"); //true
//字符串会从左开始比较第一个字符后，大小直接返回，诺一样比较下一个值。
console.log("11" > "5"); //false
//中文比较没什么意义
console.log("你" > "我"); //false
console.log("--------------------【 != == !== === 】--------------------");
console.log(10 != "10"); //false
console.log(10 == "10"); //true
console.log(true == "1"); //true
console.log(null == undefined); //true
//NaN 不跟任何值相等包括本身
var ee = NaN;
console.log(ee == NaN); //false
//是否是NaN, 需要用 isNaN() 函数判断
console.log(isNaN(ee)); //true
// !== 和 === 不会自动转换类型，所以类型和值都会做比较, 类型不一样直接返回false
console.log(10 === "10"); //false
console.log(null == undefined); //false
</script>
</head>
<body>
</body>
</html>
7. bool ? value1 : value2
<!DOCType html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript">
console.log("--------------------【 bool ? value1 : value2】--------------------");
var ff = 1==1 ? "true" : "false";
console.log(ff); //true
//取最大值
var a = 10, b = 40 ,c =30;
//不建议这么写
var max = a > b ? a > c ? a : c : b > c ? b : c;
console.log(max); //40
// 推荐方式
var max = a > b ? a : b;
max = max > c ? max : c;
console.log(max); //40
</script>
</head>
<body>
</body>
</html>
欢迎大家的意见和交流
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