<!doctype html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Document</title> </head> <body> <script> var arr = [1,2,3]; arr.four = 4; console.log(arr); arr.forEach(value => { /*if(value > 2) { break }*/ console.log(value)//1,2,3 }) for(let i in arr) { console.log(i); // '0' '1' '2' 'four' 相当于对象的key值 console.log(arr[i]) // 1,2,3,4 相当于对象的value值 } for (let i of arr) { if(i > 2) { break } console.log(i); // 1,2,3 数值中的每一项的值 console.log(arr[i]);//2,3,undefined 相当于arr[1],arr[2],arr[3] } for (let i of 'my') { console.log(i); // 'm' 'y' } for (let i of arr) { if(i > 2) { break } console.log(i); // 1,2 } </script> </body> </html>
总结：如果遍历数组最好用for of,遍历对象用for in
for of遍历数组和forEach遍历数组的区别：for of能用break语句，forEach不能