JavaScript类型转换 type conversions

2014年7月16日JavaScriptjavascript、type conversion、类型转换sheng00

var a = new Boolean(false);
console.log(a);//{}
console.log(a == false)//true
console.log(a === false)//false
if(a){
    console.log("new Boolean(false) is true")//new Boolean(false) is true
}else{
    console.log("new Boolean(false) is false")
}

这里a转换为true，因为a是一个Boolean的object，而object如果不是null或者undefined，就会被转换为true
这里主要需要分清楚值类型（primitive）和对象类型（object）
下面是JavaScript类型转换

JavaScript type conversions

值	转换为:
	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`	`"NaN"`		`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)			`true`
`[]`?(empty array)	`""`	`0`	`true`
`[9]`?(1 numeric elt)	`"9"`	`9`	`true`
`['a']`?(any other array)	use join() method	`NaN`	`true`
`function(){}`?(any function)		`NaN`	`true`

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