js判断对象是否为数组

var obj = {1:[1],2:[2]},
    arr = [1],
    str = "1";
Array.isArray(obj) // return false
Array.isArray(arr) // return true
Array.isArray(str) // return false

var obj = {1:[1],2:[2]},
    arr = [1],
    str = "1";
obj instanceof Array // return false
arr instanceof Array // return true
str instanceof Array // return false

var obj = {1:[1],2:[2]},
    arr = [1],
    str = "1";
Object.prototype.toString.call(obj); //return "[object Object]"
Object.prototype.toString.call(arr); //return "[object Array]"
Object.prototype.toString.call(str); //return "[object String]"