16.16.尚硅谷_JS基础_ 一元运算符
一、潜在作用
1、正号：对数字没啥卵用。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
var a = 123;//正正为正
a = +a ;
console.log(a);
console.log( typeof a);
var a = -123;//负正为负
a = +a ;
console.log(a);
console.log( typeof a);
</script>
</head>
<body>
</body>
</html>
2、负号：对数字惊醒负号取反
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
var a = 123;
a = -a ;
console.log(a);
console.log( typeof a);
var a = -123;//负负为正
a = -a ;
console.log(a);
console.log( typeof a);
</script>
</head>
<body>
</body>
</html>
二、真实作用：
对于非Number类型的值，它会将==先==转换为==Number==，然后再运算
- 可以对一个其他的数据类型使用 + ，来将其转换为number
- 它的原理和==Number()函数==一样
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
var a = 123;
a = true;
a = +a ;
console.log("a = " + a);
console.log(typeof a)
</script>
</head>
<body>
</body>
</html>
实际案例：(+ 可以把任何数据类型变成 number 数据类型)
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<script>
//初始状态
a = 1 + "2" + 3;
console.log("a = " + a);
console.log(typeof a)
//最终状态：
a = 1 + +"2" + 3;
console.log("a = " + a);
console.log(typeof a)
</script>
</head>
<body>
</body>
</html>
