1、循環中斷差別
具體見示例代碼：
<!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區別 </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) { //此處的return false 僅僅相當於continue
return false; //break或者continue均不能使用 會報錯，對於map filter方法一樣會報錯
//break;
//continue
} console.log(val, ' forEach') }) </script>
</body>
</html>
數組的迭代方法：every、filter、forEach、map、some均不能使用break或者continue進行中斷循環。
以上幾個函數的參數都是：一個回調函數 和 一個this的指向
array.map(function(currentValue,index,arr), thisValue)
2、數組變化時差別
（1）數組添加操作
<!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區別 </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) { //對於添加時，for可以遍歷新數組
arr.push(5) } // 輸出1 2 3 4 5
console.log(arr[i], ' for') } arr.forEach(val => { if(val == 2) { //對於添加時，forEach
arr.push(5) } // 輸出1 2 3 4 5
console.log(val, ' forEach') }) </script>
</body>
</html>
（2）數組更新、刪除操作
<!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區別 </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) { //對於更新、刪除時，for可以遍歷新數組
arr[1] = 100
//arr.splice(i,1)
} // 輸出1 100 3 4
console.log(arr[i], ' for') } arr.forEach((val, i) => { if(val == 2) { //對於更新、刪除時，forEach可以遍歷新數組
val = 100
//arr.splice(i,1)
} // 輸出1 100 3 4
console.log(val, ' forEach') }) </script>
</body>
</html>