快速數組對象取值與數組映射新數組--array.map

array.map(callback,[ thisObject]);

一、map方法的做用不難理解，「映射」嘛，也就是原數組被「映射」成對應新數組

a)array.map(()=>值);

[1,2,3].map(()=>'2323')
(3) ["2323", "2323", "2323"]

b)array.map(p=>[值,p]);

二、能夠利用map方法方便得到對象數組中的特定屬性值們

var users = [
  {name: "張含韻", "email": "zhang@email.com"},
  {name: "江一燕",   "email": "jiang@email.com"},
  {name: "李小璐",  "email": "li@email.com"}
];

var emails = users.map(function (user) { return user.email; });

undefined
emails
(3) ["zhang@email.com", "jiang@email.com", "li@email.com"]

三、Array.prototype擴展可讓IE6-IE8瀏覽器也支持map方法：

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