This article mainly introduces the implementation method of using trackBy to improve performance in Angular. Friends who need it can refer to it
When traversing a collection (collection) in Angular template, you would write like this :
<ul> <li *ngFor="let item of collection">{{item.id}}</li> </ul>
Sometimes you will need to change this collection, such as returning new data from the backend interface. Then the problem comes, Angular doesn't know how to track the items in this collection, and doesn't know which ones should be added, which should be modified, and which ones should be deleted. As a result, Angular will remove all items from the collection and then add them again. Like this:
#The disadvantage of this is that it will perform a large number of DOM operations, and DOM operations are very performance-consuming.
The solution is to add a trackBy function to *ngFor to tell Angular how to track each item of the collection. The trackBy function takes two parameters, the first is the index of the current item, the second is the current item, and returns a unique identifier, like this:
import{ Component } from '@angular/core'; @Component({ selector: 'trackBy-test', template: ` <ul><li *ngFor="let item of items; trackBy: trackByIndex">{{item.name}}</li></ul> <button (click)="getItems()">Get Items</button> ` }) export class TrackByCmp{ items: any[]=[]; constructor(){ this.items = [{name:'Tom'},{name:'Jerry'},{name:'Kitty'}]; } getItems(){ this.items = [{name:'Tom'},{name:'Jerry'},{name:'Mac'},{name:'John'}]; } trackByIndex(index, item){ return index; } }
After doing this, Angular knows which items Changed:
#We can see that the DOM only redraws the modified and added items. Moreover, clicking the button again will not redraw it. But when the trackBy function is not added, repeated clicks on the button will still trigger redrawing (you can look back at the first GIF).
The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.
Related articles:
Use native JavaScript to achieve the magnifying glass effect
Encapsulated cache class implemented through redis as a cache in nodejs
Use bcryptjs password encryption in Express
Use icon icon through Element in Vue
Use How does Vue.set() implement dynamic response to data
How to implement dynamic binding of images and data return image paths in vue
The above is the detailed content of How to improve performance using trackBy in Angular. For more information, please follow other related articles on the PHP Chinese website!

本篇文章继续Angular的学习,带大家了解一下Angular中的元数据和装饰器,简单了解一下他们的用法,希望对大家有所帮助!

本篇文章带大家深入了解一下angular的状态管理器NgRx,介绍一下NgRx的使用方法,希望对大家有所帮助!

angular中怎么使用monaco-editor?下面本篇文章记录下最近的一次业务中用到的 monaco-editor 在 angular 中的使用,希望对大家有所帮助!

Angular项目过大,怎么合理拆分它?下面本篇文章给大家介绍一下合理拆分Angular项目的方法,希望对大家有所帮助!

怎么自定义angular-datetime-picker格式?下面本篇文章聊聊自定义格式的方法,希望对大家有所帮助!

本篇文章给大家分享一个Angular实战,了解一下angualr 结合 ng-zorro 如何快速开发一个后台系统,希望对大家有所帮助!

Angular Route中怎么提前获取数据?下面本篇文章给大家介绍一下从 Angular Route 中提前获取数据的方法,希望对大家有所帮助!

本篇文章带大家了解一下Angular中的独立组件,看看怎么在Angular中创建一个独立组件,怎么在独立组件中导入已有的模块,希望对大家有所帮助!


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

SublimeText3 Chinese version
Chinese version, very easy to use

SublimeText3 Mac version
God-level code editing software (SublimeText3)

MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

Dreamweaver CS6
Visual web development tools

DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software
