What are the precautions for using Dom in Angular2?

This time I will bring you what are the precautions for using Dom in Angular2, and what are the precautions for using Dom in Angular2. The following is a practical case, let's take a look.

Preface

The design goal of Angular2 is to make the browser and DOM independent. The DOM is complex, so decoupling components from it will make our applications easier to test and refactor. In order to support cross-platform, Angular also encapsulates the differences of different platforms through abstraction.

Content

#1. Why can’t the DOM be manipulated directly?

Angular2 adopts AOT static compilation mode. In this form, our template type must be stable and safe. Directly using javascript and jquery languages ​​​​is unstable because their compilation will not be discovered in advance. Error, so angular2 will choose the typescript language, which is a superset of javascript (errors can be found during compilation of this language).

2. Three incorrect ways to operate DOM:

@Component({ ... })
export class HeroComponent {
 constructor(private _elementRef: ElementRef) {}
 doBadThings() {
  $('id').click(); //jquery
  this._elementRef.nativeElement.xyz = ''; //原生的ElementRef
  document.getElementById('id'); //javascript
 }
}

3. What is the mechanism of DOM operation in Angular2?

In order to support cross-platform, Angular encapsulates the differences of different platforms through abstraction layers. For example, abstract classes Renderer, Renderer2, abstract class RootRenderer, etc. are defined. In addition, the following reference types are defined: ElementRef, TemplateRef, ViewRef, ComponentRef, ViewContainerRef, etc.

4. Correct way to operate DOM (ElementRef and Renderer2):

product.component.html

商品信息

 

  {{product.title}}
 

product.component.ts

import { Component, OnInit,Renderer2, ViewChild，ElementRef,AfterViewInit} from '@angular/core';
@Component({
 selector: 'app-product',
 templateUrl: './product.component.html',
 styleUrls: ['./product.component.css']
})
export class ProductComponent implements OnInit,AfterViewInit {
 @ViewChild('dia') dia:ElementRef ;定义子试图
 ngOnInit() {
 /**1.
 *创建一个文本
 */
  this.dia.nativeElement.innerHTML="这只是一个测试的文档";
 /**2.
  *添加click事件
  */
 let ul=this.element.nativeElement.querySelector('ul');
  this.render2.listen(ul,"click",()=>{
   this.render2.setStyle(ul,"background","blue");
ngAfterViewInit(){
/**3.
 *修改背景颜色
 */
 let li=this.element.nativeElement.querySelector('ul');
 this.render2.setStyle(li,"background","red");
 }
}

Summary

In fact, when learning a language, we should first follow its specifications, accept the differences between it and the previous language, and then deeply understand the differences between it and the previous language. What is the difference in the method and why do we do this? Otherwise we cannot understand the beauty of this language. I hope it will be helpful to you!

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!

Recommended reading:

Operation AngularJS from scratch to implement application modularization

How to use vue to make a single-page application Front-end routing

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