sort: 用in-place 演算法對陣列的元素進行排序，並返回陣列

語法: arr.sort(compareFunction)
          compareFunction 可選，如果省略，元素根據字串Unicode碼點進行預設排序
          compareFunction(a, b) 小於 0 ，那麼 a 會被排列到 b 之前
          compareFunction(a, b) 等於 0 ， a 和 b 的相對位置不變(不保證所有瀏覽器順序一定這樣)
          compareFunction(a, b) 大於 0 ， b 會被排列到 a 之前

(1) 比較數字

var number = [21,37,45,-12,0,37];
// number.sort((a,b) => a - b); //升序排列
number.sort((a,b) => b - a); //降序排列
console.log(number); //[45, 37, 37, 21, 0, -12]

(2) 比較物件

 var items = [
       { name: 'Edward', value: 21 },
       { name: 'Sharpe', value: 37 },
       { name: 'And', value: 45 },
       { name: 'The', value: -12 }, 
       { name: 'Magnetic',value: 0 },
       { name: 'Zeros', value: 37 } 
];
items.sort( (a, b) => a.value - b.value);
 

map

語法：array.map(function(value, index, array) {// ...});

(1) 原陣列被“對映”成對應新陣列

var data = [1, 2, 3, 4];
var arrayOfSquares = data.map(function (item) {
    return item * item;
});
console.log(arrayOfSquares); // 1, 4, 9, 16

(2) 獲得物件陣列中的特定屬性值

var users = [
    {name: "張一", "email": "[email protected]
 
"},
    {name: "江二",   "email": "[email protected]"},
    {name: "李三",  "email": "[email protected]"}
];
var emails = users.map(function (user) { return user.email; });
console.log(emails.join(", ")); // [email protected], [email protected], [email protected] 

(3)向物件陣列新增屬性

 var users = [
    {name: "張一", "email": "[email protected]"},
    {name: "江二",   "email": "[email protected]"},
    {name: "李三",  "email": "[email protected]"}
 ];
 users  = users.map(function (user,index) { 
       user.index = index;
       return user; 
 });
 console.log(JSON.stringify(users)); // [{"name":"張一","email":"[email protected]","index":0},{"name":"江二","email":"[email protected]","index":1},{"name":"李三","email":"[email protected]","index":2}]