js类型转换
js类型
在了解类型之后，再去了解==与===的区别
==如果之比较“转化成同一类型后的值”看“值”是否相等，===如果类型不同，其结果就是不等。也就是从根本上比较类型。
对于Array,Object等高级类型，==和===是没有区别的进行“指针地址”比较
- boolean
- number
- string
- object
看下面表格一目了然：
| Value | Converted to: | |||
|---|---|---|---|---|
| String: | Number | Boolean | Object | |
| undefined | "undefined" | NaN | false | throws TypeError |
| null | "null" | 0 | false | throws TypeError |
| true | "true" | 1 | new Boolean(true) | |
| false | "false" | 0 | new Boolean(false) | |
| "" (empty string) | 0 | false | new String("") | |
| "1.2" (nonempty, numeric) | 1.2 | true | new String("1.2") | |
| "one" (nonempty, non-numeric) | NaN | true | new String("one") | |
| 0 | "0" | false | new Number(0) | |
| -0 | "0" | false | new Number(-0) | |
| NaN | "undefined" | false | new Number(NaN) | |
| Infinity | "Infinity" | true | new Number(Infinity) | |
| -Infinity | "-Infinity" | true | new Number(-Infinity) | |
| 1 (finite, non-zero) | "1" | true | new Number(1) | |
| {} (any object) | NaN | true | ||
| [] (empty array) | "" | 0 | true | |
| [9] (1 numeric elt) | "9" | 9 | true | |
| ['a'] (any other array) | use join() method | NaN | true | |
| function(){} (any function | "undefined" | NaN | true |