數組新增常用方法map，reduce，filter，forEach

map映射

let arr=[66,59,80];
let result=arr.map(item => {
if(item >= 60){
  return "及格"
}else{
  return "不及格"
}
});
//result:["及格", "不及格", "及格"]

reduce --彙總

let arr = [12,69,180,8763];
let result = arr.reduce((tmp, item, index) => {
 console.log(tmp, item, index);
 return tmp + item;
 });
 console.log(result);//求和

filter --過濾

let arr=[
    {title: '電源線', price: 50},
    {title: '電腦', price: 13000},
    {title: '鍵盤', price: 120},
    {title: '手機', price: 9000}
];
 
let result=arr.filter(json=>json.price>=5000);
 
console.log(result);//[{title: '電腦', price: 13000},{title: '手機', price: 9000}]

forEach --迭代

let arr=[12,5,8,9];
 
arr.forEach((item,index)=>{
   console.log(index+': '+item); //0: 12  1: 5  2: 8  3: 9
});