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