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 |
|
