angular OnChange事件

import { Component, OnInit, Input, OnChanges, SimpleChanges } from '@angular/core';

@Component({
  selector: 'app-child',
  templateUrl: './child.component.html',
  styleUrls: ['./child.component.css']
})
export class ChildComponent implements OnInit, OnChanges {

  @Input()
  greeting: string;

  @Input()
  user: {};

  message = 'hello';

  constructor() { }

  ngOnInit() {
  }

  ngOnChanges(changes: SimpleChanges): void {
    console.log(JSON.stringify(changes, null, ));
  }

}

<div>子组件</div>
<p>问候语{{greeting}}</p>
<p>用户{{user.name}}</p>
<input [(ngModel)]='message'>

import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  greeting = 'nihao';
  user: { name: string } = { name: 'cys' };
}

<input [(ngModel)]="greeting" type="text">
<input [(ngModel)]="user.name" type="text">
<app-child [greeting]="greeting" [user]="user"></app-child>