let arr = [‘a‘, ‘b‘, ‘c‘, ‘d‘] arr.forEach(function (val, index, arr) { console.log(‘index:‘+index+‘,‘+‘val:‘+val) // val是当前元素，index当前元素索引，arr数组 console.log(arr) }) //index:0,val:a //["a", "b", "c", "d"]0: "a"1: "b"2: "c"3: "d" //index:1,val:b //["a", "b", "c", "d"] //index:2,val:c //["a", "b", "c", "d"] //index:3,val:d //["a", "b", "c", "d"]
for in
let arr = [1,2,3,4]; arr.b=‘100‘; for(let key in arr){ console.log(key);//会把b输出来 }
for of
原文：https://www.cnblogs.com/theblogs/p/10520590.html