1：map 俗稱對映

    let arr=[12,5,8];
    let result=arr.map(item => item*2);
    console.log(result);// [24, 10, 16]

  let score=[19, 85, 99, 25, 90];

  let result=score.map(item=>item>=60?'及格':'不及格');
  console.log(result); //不及格,及格,及格,不及格,及格

2：reduce：俗稱累加

    let arr=[10,25,32,41];
    let sum=arr.reduce(function (tmp, item, index){
      //alert(tmp+','+item+','+index);
      console.log(tmp+';'+item+';'+index+';');
      //10;25;1;
      //35;32;2;
      //67;41;3;
      return tmp+item;
    });  
    console.log(sum); // 求和  108 

    let ave=arr.reduce(function (tmp, item, index){
      if(index!=arr.length-1){ //不是最後一次
        return tmp+item;
      }else{                    //最後一次
        return (tmp+item)/arr.length;
      }
    });
    console.log(ave); // 求平均值  27
 

    let arr=[12,5,8,99,27,36,75,11];
    let result=arr.filter(item=>item%3==0);
    console.log(result);[12, 99, 27, 36, 75]

    let arr=[
      {title: '男士襯衫', price: 75},
      {title: '女士包', price: 57842},
      {title: '男士包', price: 65},
      {title: '女士鞋', price: 27531}
    ];

    let result=arr.filter(json=>json.price>=10000);

    console.log(result);//{title: "女士包", price: 57842} {title:"女士鞋",price: 27531}
 

4：forEach：遍歷

    let arr=[12,5,8,9];

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