1、循环中断差别
具体见示例代码：
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<title>js for forEach区别 </title>
</head>
<body>
<script src="https://cdn.bootcss.com/lodash.js/4.17.10/lodash.min.js"></script>
<script type="text/javascript"> let arr = [1, 2, 3, 4] for(let i = 0; i < arr.length; i++) { if(arr[i] == 2) { continue; //break;
} console.log(arr[i], ' for') } for(let i in arr) { if(i == 2) { break; } console.log(arr[i], ' for in') } for(let i of arr) { if(i == 2) { break; } console.log(i, ' for of') } arr.forEach(val => { if(val == 2) { //此处的return false 仅仅相当于continue
return false; //break或者continue均不能使用 会报错，对于map filter方法一样会报错
//break;
//continue
} console.log(val, ' forEach') }) </script>
</body>
</html>
数组的迭代方法：every、filter、forEach、map、some均不能使用break或者continue进行中断循环。
以上几个函数的参数都是：一个回调函数 和 一个this的指向
array.map(function(currentValue,index,arr), thisValue)
2、数组变化时差别
（1）数组添加操作
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<title>js for forEach区别 </title>
</head>
<body>
<script src="https://cdn.bootcss.com/lodash.js/4.17.10/lodash.min.js"></script>
<script type="text/javascript"> let arr = [1, 2, 3, 4] for(let i = 0; i < arr.length; i++) { if(arr[i] == 2) { //对于添加时，for可以遍历新数组
arr.push(5) } // 输出1 2 3 4 5
console.log(arr[i], ' for') } arr.forEach(val => { if(val == 2) { //对于添加时，forEach
arr.push(5) } // 输出1 2 3 4 5
console.log(val, ' forEach') }) </script>
</body>
</html>
（2）数组更新、删除操作
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<title>js for forEach区别 </title>
</head>
<body>
<script src="https://cdn.bootcss.com/lodash.js/4.17.10/lodash.min.js"></script>
<script type="text/javascript"> let arr = [1, 2, 3, 4] for(let i = 0; i < arr.length; i++) { if(arr[i] == 2) { //对于更新、删除时，for可以遍历新数组
arr[1] = 100
//arr.splice(i,1)
} // 输出1 100 3 4
console.log(arr[i], ' for') } arr.forEach((val, i) => { if(val == 2) { //对于更新、删除时，forEach可以遍历新数组
val = 100
//arr.splice(i,1)
} // 输出1 100 3 4
console.log(val, ' forEach') }) </script>
</body>
</html>