js-map

Contents

1. 1. map
   1. 1.1. 兼容性–改进:

map

map将原来的数据映射成新数组；

var arr = [1,2,3,4];

var arr2 = arr.map(function(item){return item;});

console.log(arr2);
//[1, 2, 3, 4]

console.log(typeof arr2); //"object"

声明一个userInfo数组对象：

var userInfo = [
    {"name": "lmo", "email": "lmo@lmo.space"},
    {"name": "lomo1", "email": "lomo1@lomo1.spae"},
    {"name": "lomo", "email": "lomo@lomo.space"},
    {"name": "lomo2", "email": "lomo2@lomo2.space"}
];

使用map取出特定属性值的集合。

var users = userInfo.map(function(item){return item;});
users.length; // 4

var usersName = userInfo.map(function(item){return item.name;});
console.log(usersName); //["lmo", "lomo1", "lomo", "lomo2"]

var usersEmail = userInfo.map(function(item){return item.email;});
usersEmail; //object->["lmo@lmo.space", "lomo1@lomo1.spae", "lomo@lomo.space", "lomo2@lomo2.space"]

console.log(usersEmail.join(","));
//输出： lmo@lmo.space,lomo1@lomo1.spae,lomo@lomo.space,lomo2@lomo2.space

兼容性–改进:

IE6 ~ IE8

Array.prototype.map map方法的根->Array；

if(typeof Array.prototype.mar != "function")
{
    Array.prototype.map = function(fn, context){
        var arr = [];
        if(typeof fn === "function")
        {
            //不能使用let k = 0;
            for(var k = 0; k < this.length; k ++)
            {
                arr.push(fn.call(context, this[k], this));
            }
        }
        return arr;
    };
}