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  • 关于for循环

    1、普通for循环 (遍历数组的索引值(下标),边界可以自己划定)

    var arr = [10, 20, 30];
    for(var i=0; i<arr.length; i++)
      console.log(arr[i]); //10 20 30

    2、for-in 循环(遍历数组或者对象的索引值(key值))(IE 6+)

    var arr = [10, 20, 30];
    var obj = {
        "a": 40,
        "b": 50,
        "c": 60
      };
    var i;

    for(i in arr){
      console.log(i);  //0 1 2
      console.log(arr[i]);  //10 20 30
    }

    for(i in obj){
      console.log(i);  //"a" "b" "c"
      console.log(obj[i]);  //40 50 60
    }

    3、for-of循环(不适用于对象,遍历得到Set、Map、数组的value)(IE不支持)

    var arr = [10, 20, 30];
    var set = new Set([40, 50, 60]);
    var map = new Map([
      ["a", 10],
      ["b", 20],
      ["c", 30]
    ]);
    var val;
    for(val of arr)
      console.log(val);  //10 20 30;
    for(val of set)
      console.log(val);  //40, 50 60
    for(val of map)
      console.log(val);  //["a": 10] ["b": 20] ["c": 30]

    4、forEach 循环  (不适用于对象) (IE9+)

    var arr = [10, 20, 30];
    var set = new Set([40, 50, 60]);
    var map = new Map([
      ["a", 10],
      ["b", 20],
      ["c", 30]
    ]);
    arr.forEach((val, index, ele) => {
      console.log(index + ":" + val);  //0:10 1:20 2:30
      console.log(ele)  //[10,20,30] ~ ~
    })
    set.forEach((val, index, ele) => {
      console.log(index + ":" + val);  //40:40 50:50 60:60
      console.log(ele)  //Set(3) {40, 50, 60} ~~~ ~~~
    })
    map.forEach((val, index, ele) => {
      console.log(index + ":" + val);  //"a":10 "b":20 "c":30
      console.log(ele)  //Map(3) {"a" => 10, "b" => 20, "c" => 30} ~~~~ ~~~~
    })
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  • 原文地址:https://www.cnblogs.com/lianchenxi/p/9600472.html
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