js创建及操作数组

var colors = new Array();
创建length值为20的的数组： var colors = new Array(20);
直接传递数组的项： var colors = new Array("red", "blue", "green");

 var colors = ["red", "blue", "green"];

colors[2] = "black"   //修改第三项

colors[3] = "brown"  //新增第四项

colors.length = 2;   //数组长度缩短为2

colors[colors.length] = "white" //设置最后一项

if(value instanceof Array){

　　//执行某些操作

}

if(Array.isArray(value)){

  //对数组执行某些操作(ie9+)

}

var colors = ["red", "blue", "green"];
 alert(colors.toString());   //red,blue,green以逗号分隔的字符串
 alert(colors.valueOf());    //red,blue,green返回的是数组
 alert(colors);              //red,blue,green

var colors2 = ["red", "blue", "green"];
 alert(colors2.join(","));    //red,blue,green
 alert(colors2.join("||"));   //red||blue||green

var colors = new Array();
var count = colors.push("red","blue","green");  //向后插入两项
alert(count);            //3
alert(colors);           //red,blue,green

var item = colors.pop();                //移除最后一项并返回
alert(item);            //green
alert(colors.length)    //2

var item2 = colors.shift();             //移除第一项并返回
alert(item2);           //red
alert(colors.length)    //1

var count2 = colors.unshift("black","white");
alert(count2);          //3
alert(colors);          //black,white,blue

var values = [0,1,5,10,15];
values.reverse();       //翻转数组
alert(values);          //15,10,5,1,0
values.sort();          //升序排列，先调用tostring（）将数组项转换成字符串，然后比较字符串。
alert(values);          //0,1,10,15,5

values.sort(compare);   //加入比较函数
alert(values)           //0,1,5,10,15

function compare(value1,value2){
    return value1 - value1;   //降序
}