zoukankan      html  css  js  c++  java
  • js 如何让forEach可以break?

    While working with Java Script, all of us must have surely run into the case where we need to loop through an array and break the running loop if a certain condition is met. There are many methods how we can loop through an array but we are always looking for the most efficient way to do that.

    Our favorite loop method: Array.prototype.forEach

    forEach is such an useful method.
    But…how can I break the forEach loop?
    Well… you can’t break forEach.

    1
    2
    3
    4
    5
    6
    var arr = ["Kathmandu", "Pokhara", "Lumbini", "Gorkha"];
     
    arr.forEach(function(value, index, _arr) {
    console.log(index + ": " + value);
    return false;
    });

    The result should look like

    1
    2
    3
    4
    0: Kathmandu
    1: Pokhara
    2: Lumbini
    3: Gorkha

    It’s still iterating through all items in the array. What should I do if I want to stop the loop based on the condition? We either set a variable that changes only if the condition is met, but it will still mean that the loop will iterate until the array is exhausted to the last item.

    So, what do we do?? It’s simple.

    Don’t use “forEach”. Use “some” or “every”.


    Array.prototype.some

    Array.prototype.some is pretty much the same as forEach but it break when the callback returns true.

    Example:

    1
    2
    3
    4
    5
    6
    var arr= ["Kathmandu", "Pokhara", "Lumbini", "Gorkha"];
     
    arr.some(function (value, index, _arr) {
    console.log(index + ": " + value);
    return value === "Pokhara";
    });

    The result should look like

    1
    2
    0: Kathmandu
    1: Pokhara

    What happened here? Since the third iteration returned true, we successfully stopped the loop!


    Array.prototype.every

    Array.prototype.every is almost identical to some except it’s expecting false to break the loop.

    Example:

    1
    2
    3
    4
    5
    6
    var arr = ["Kathmandu", "Pokhara", "Lumbini", "Gorkha"];
     
    arr.every(function(value, index, _arr) {
    console.log(index + ": " + value);
    return value.indexOf("Lumbini") < 0;
    });

    The result should look like

    1
    2
    3
    0: Kathmandu
    1: Pokhara
    2: Lumbini

    What happened here? Since the third iteration returned false, we successfully stopped the loop!

    Now you can break loops whenever you want! Enjoy.

    Source:http://sajanmaharjan.com.np/2016/08/12/javascript-break-foreach/

  • 相关阅读:
    Ionic4.x 中的button
    Ionic4.x 内置颜色
    Ionic4.x 中自定义公共模块
    Ionic4.x 新增底部 tabs 页面
    Ionic4.x 创建页面以及页面跳转
    Ionic4.x 项目结构简单分析
    判断Activty是否在前台运行
    Ionic 的安装运行
    Angular 自定义模块以及配置路由实现模块懒加载
    Angular 自定义模块
  • 原文地址:https://www.cnblogs.com/backuper/p/10251398.html
Copyright © 2011-2022 走看看