function add(x, y, f) {
    return f(x) + f(y);
}
//當調(diào)用add(-5, 6, Math.abs)時，參數(shù)x，y和f分別接收-5，6和函數(shù)Math.abs，根據(jù)函數(shù)定義，可以推導計算過程為：
//x = -5;
//y = 6;
//f = Math.abs;
//f(x) + f(y) ==> Math.abs(-5) + Math.abs(6) ==> 11;
//return 11;

//用代碼驗證一下：
add(-5, 6, Math.abs); // 11

 function pow(x) {
            return x * x;
        }

        var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
        alert (arr.map(pow))

let arr=[6,8,8,6,9,6]
        let a=arr.reduce(function(x,y){
            return x+y;
        })
        alert(a)

var arr = [1,2,1,2,1,2,1,2];
        var r = arr.filter(function (x) {
            return x % 2 == 0;
        });
        alert(r)

//從小到大排列
 let arr=[1,3,1,2,3,6,4,3]
        let arr1=arr.sort((a,b)=>a-b)
        alert(arr1)

//從大到小排列
 let arr=[1,3,1,2,3,6,4,3]
        let arr1=arr.sort((a,b)=>b-a)
        alert(arr1)

let arr=[4,6,8,8]
        let result=arr.every(function(a){
            return a>6
        })
        alert(result)

let arr=[4,6,8,9]
        let result=arr.find(function(a){
            return a>6
        })
        alert(result)

 let arr=[4,6,8,9]
        let result=arr.findIndex(function(a){
            return a>6
        })
        alert(result)

const items = ['item1', 'item2', 'item3'];
const copy = [];
//傳統(tǒng)方式
for (let i=0; i<items.length; i++) {
  copy.push(items[i]);
}
// foreach方法
items.forEach(function(item){
  copy.push(item);
});