Some methods javascript object

1. Detection property

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in operator: if the inherited properties or attributes of its own object contains this property returns true

	var o={x:1};
	"x" in o;//true
	"y" in o;//false
	"toString" in o;true

hansOwnProperty (): detects whether the property is owned property of an object

var o={x:1}
	o.hansOwnProperty("x");//true
	o.hansOwnProperty("y");//false
	o.hansOwnProperty("toString");//false

!==可以区分undefined和null 

2. Enumerated attribute

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for / in loop can traverse the object can be enumerated attributes: its own property and inherit property

	for(p in o){
		if(!o.hanOwnProperty(p)) continue;//跳过继承属性
	}
	for(p in o){
		if(typeof o[p] ==="function") continue;//跳过方法
	}

3. Get the name of the object properties

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	Object.keys()//返回一个数组，由对象中可枚举的属性名称组成，
	Object.getOwnPropertyNames()//返回对象中所有自有属性的名称