import {Component, ElementRef, OnInit} from '@angular/core';
@Component({
 selector: 'app-root',
 templateUrl: './app.component.html',
 styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit{
 color:string;
 title = 'button !';
 constructor(private el:ElementRef){}
 setHeight(){
  this.el.nativeElement.querySelector('.btn1').style.height = '300px';
 }
 ngOnInit(){
  this.setHeight();
 }
}

<h1>
 {{title}}
</h1>
<div>
<button myHighlight class="btn btn1">按钮一</button>
<button myHighlight class="btn">按钮二</button>
<button myHighlight class="btn">按钮三</button>
</div>

<h1>
 {{title}}
</h1>
<div>
<button myHighlight class="btn btn1">按钮一</button>
<button myHighlight class="btn" #btn>按钮二</button> <!--增加一个变量-->
<button myHighlight class="btn">按钮三</button>
</div>

import {Component, ElementRef, OnInit, ViewChild} from '@angular/core';
@Component({
 selector: 'app-root',
 templateUrl: './app.component.html',
 styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit{
 @ViewChild('btn') btn:ElementRef;//通过@ViewChild获取元素
 color:string;
 title = 'button !';
 constructor(private el:ElementRef){}
 setHeight(){
  this.el.nativeElement.querySelector('.btn1').style.height = '300px';
 }
 setWidth(){
  this.btn.nativeElement.style.width = '200px';//定义宽度
 }
 ngOnInit(){
  this.setHeight();
  this.setWidth();
 }
}

import {Component, ElementRef, OnInit, Renderer2, ViewChild} from '@angular/core';
@Component({
 selector: 'app-root',
 templateUrl: './app.component.html',
 styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit{
 @ViewChild('btn') btn:ElementRef;
 color:string;
 title = 'button !';
  //初始化renderer2
 constructor(private el:ElementRef,private renderer2: Renderer2){}
 setHeight(){
  this.el.nativeElement.querySelector('.btn1').style.height = '300px';
 }
 setWidth(){
  // this.btn.nativeElement.style.width = '200px';
  
  //使用renderer2的setStyle方法设置宽度
  this.renderer2.setStyle(this.btn.nativeElement,'width','200px')
 }
 ngOnInit(){
  this.setHeight();
  this.setWidth();
 }
}

class Renderer2 {
 data : {[key: string]: any}
 destroy() : void
 createElement(name: string, namespace?: string) : any
 createComment(value: string) : any
 createText(value: string) : any
 destroyNode : (node: any) => void |
 appendChild(parent: any, newChild: any) : void
 insertBefore(parent: any, newChild: any, refChild: any) : void
 removeChild(parent: any, oldChild: any) : void
 selectRootElement(selectorOrNode: string|any) : any
 parentNode(node: any) : any
 nextSibling(node: any) : any
 setAttribute(el: any, name: string, value: string, namespace?: string) : void
 removeAttribute(el: any, name: string, namespace?: string) : void
 addClass(el: any, name: string) : void
 removeClass(el: any, name: string) : void
 setStyle(el: any, style: string, value: any, flags?: RendererStyleFlags2) : void
 removeStyle(el: any, style: string, flags?: RendererStyleFlags2) : void
 setProperty(el: any, name: string, value: any) : void
 setValue(node: any, value: string) : void
 listen(target: 'window'|'document'|'body'|any, eventName: string, callback: (event: any) => boolean | void) : () => void
}