[JavaScript] JS中如何跳出循环/结束遍历

[JavaScript] JS中如何跳出循环/结束遍历

直接抛结论，下表是JS中常用的实现循环遍历的方法的跳出/结束遍历的办法，经过测试后的总结。可能各位大佬还有其他的办法，我在此表示大佬NB。

1. for循环

var arr = ['a', 'b', 'c', 'd', 'e'];
var show = [];
 
for (var i = 0; i < arr.length; i++) {
    if (i === 2) {
        break;// ['a', 'b'] 成功跳出循环
        // continue;// ['a', 'b', 'd', 'e'] 只能跳出本次循环
        // return;// Uncaught SyntaxError: Illegal return statement
        // return true;// Uncaught SyntaxError: Illegal return statement
        // return false;// Uncaught SyntaxError: Illegal return statement
    }
    show.push(arr[i]);
}

2. Array.forEach()

var arr = ['a', 'b', 'c', 'd', 'e'];
var show = [];
 
arr.forEach((item, index) => {
    if (index === 2) {
        // break;// Uncaught SyntaxError: Illegal break statement
        // continue;// Uncaught SyntaxError: Illegal continue statement: no surrounding iteration statement
        // return;// ["a", "b", "d", "e"] 只能跳出本次循环
        // return true;// ["a", "b", "d", "e"] 只能跳出本次循环
        // return false;// ['a', 'b', 'd', 'e'] 只能跳出本次循环
    }
    show.push(item);
})

3. for...in...

var arr = ['a', 'b', 'c', 'd', 'e'];
var show = [];
 
for (var item in arr) {
    if (item === '2') {
        break;// ["a", "b"] 跳出循环成功
        // continue;// ["a", "b", "d", "e"] 只能跳出本次循环
        // return;// Uncaught SyntaxError: Illegal return statement
        // return true;// Uncaught SyntaxError: Illegal return statement
        // return false;// Uncaught SyntaxError: Illegal return statement
    }
 
    show.push(arr[item]);
}

4. Array.map()

var arr = ['a', 'b', 'c', 'd', 'e'];
var show = [];
 
arr.map((item, index) => {
    if (index === 2) {
        // break;// Uncaught SyntaxError: Illegal break statement
        // continue;// Uncaught SyntaxError: Illegal continue statement: no surrounding iteration statement
        // return;// ["a", "b", "d", "e"] 只能跳出本次循环
        // return true;// ["a", "b", "d", "e"] 只能跳出本次循环
        // return false;// ["a", "b", "d", "e"] 只能跳出本次循环
    }
    show.push(item);
})

5. Array.some()

var arr = ['a', 'b', 'c', 'd', 'e'];
var show = [];
 
arr.some((item, index) => {
    if (index === 2) {
        // break;// Uncaught SyntaxError: Illegal break statement
        // continue;// Uncaught SyntaxError: Illegal continue statement: no surrounding iteration statement
        // return;// ["a", "b", "d", "e"] 只能跳出本次循环
        return true;// ["a", "b"] 成功跳出循环
        // return false;// ["a", "b", "d", "e"] 只能跳出本次循环
    }
    show.push(item);
})

6. Array.every()

var arr = ['a', 'b', 'c', 'd', 'e'];
var show = [];
 
arr.every((item, index) => {
    if (index === 2) {
        // break;// Uncaught SyntaxError: Illegal break statement
        // continue;// Uncaught SyntaxError: Illegal continue statement: no surrounding iteration statement
        // return;// ["a", "b"] 成功跳出循环
        // return true;// ["a", "b", "d", "e"] 只能跳出本次循环
        return false;// ["a", "b"] 成功跳出循环
    }
    return show.push(item);
})

some()与 every()不同，some遍历中一个为真全部即为真，而every遍历中全部为真才行。some遍历中返回 true才会退出执行，而every则需要返回 false才会退出执行。

7. Array.filter()

var arr = ['a', 'b', 'c', 'd', 'e'];
var show = [];
 
arr.filter((item, index) => {
    if (index === 2) {
        // break;// Uncaught SyntaxError: Illegal break statement
        // continue;// Uncaught SyntaxError: Illegal continue statement: no surrounding iteration statement
        // return;// ["a", "b", "d", "e"] 只能跳出本次循环
        // return true;// ["a", "b", "d", "e"] 只能跳出本次循环
        return false;// ["a", "b", "d", "e"] 只能跳出本次循环
    }
    show.push(item);
})