JS for-in语句的使用

JS for-in语句的使用

js中for循环一般用于遍历数组

for-in一般用于循环遍历对象的属性

　　
　　因为JavaScript的数组其实就是对象，它把数组的下标转变成字符串，用其作为属性。所以下面两个对象类似：

//数组字面量
var numbers=["zero","one","two","three","four","five"];
//它很类似对象字面量
var numbers_object={
	"0":"zero","1":"one","2":"two",3:"three",4:"four","5":"five"
}

　　因为JavaScript的数组其实就是对象,所以for in语句可以用来遍历一个对象的所有属性，即：

var numbers=["zero","one","two","three","four","five"];
//num只是该数组对象的属性
for(var num in numbers){
	console.log(num);//0,1,2,3,4,5 
}
//这样才能得到数组中的每一项
for(var num in numbers){
	console.log(numbers[num]);//"zero","one","two","three","four","five"
}

　　但要注意for-in无法保证属性的顺序。