隐式创建(字面量创建)
var arr=["RED","GREEN","BLUE"];
直接实例化(构造函数创建)
var arr=new Array("RED","GREEN","BLUE");
创建数组并给数组元素赋值
var arr=new Array();
arr[0]="RED";
arr[1]="GREEN";
arr[2]="BLUE";
注意：
console.log(arr.length); //3
arr[4]='jeep';
console.log(arr.length); //5
console.log(arr[3]); //undefined
