child.html

<p>child4 works!</p><div class="us">我是歌谣</div>
<div [ngClass]="currentClass" class="col">我是歌谣</div><div *ngIf="true">aaaa</div>
<div *ngIf="false">bbbbb</div>

child.ts

import { Component, OnInit } from '@angular/core';@Component({selector: 'app-child4',templateUrl: './child4.component.html',styleUrls: ['./child4.component.css']
})
export class Child4Component implements OnInit {
currentClass(){}constructor() { }ngOnInit(): void {this.currentClass={col:true}}}

运行结果