Array一些api的用法

一、Array.forEach() 遍历

没有返回值

var a = [20,30,40]
a.forEach(function(value,key,arr){
	console.log(value+","+key+",["+arr+"]")
})
//"20,0,[20,30,40]"
//"30,1,[20,30,40]"
//"40,2,[20,30,40]"

二、Array.sort() 排序

var a = [1,3,6,9,2,7];
a.sort(function(x,y){return x-y})       //[1, 2, 3, 6, 7, 9]
a.sort(function(x,y){return y-x})       //[9, 7, 6, 3, 2, 1]

三、Array.filter 过滤

var a = [1,2,3,4,5,6]
a.filter(function(x){return x > 3})      //[4,5,6]

四、Array.join 以什么作为间隔合并成字符串

var a = [1,2,3]
a.join("--")    //"1--2--3"

五、Array.concat 合并数组

var a = [1,2,3],b=[4,5,6,7]
a.concat(b)    //[1,2,3,4,5,6,7]

六、Array.map 返回一个处理后的数组

var a = [1,2,3]
a.map(function(x){return x*2})    //[2,4,6]

七、Array.reduce

var a = [1,2,3]
//可替代map
a.reduce(function(arr,n){
	arr.push(n*2);
	return arr
},[])
//[2,4,6]

a.reduce(function(a,b){	
	return a+b
})
//6