1. 在组件类中，为每个表单控件添加一个值变化事件处理程序。例如：

HTML：

TypeScript：

export class MyComponent {
  user = {
    firstName: '',
    lastName: ''
  };

  onFirstNameChange(value: string) {
    console.log('First name changed to:', value);
  }

  onLastNameChange(value: string) {
    console.log('Last name changed to:', value);
  }
}

2. 使用valueChanges方法的pluck操作符，获取特定表单控件的值更改。例如：

HTML：

TypeScript：

import { Component } from '@angular/core';
import { FormGroup, FormBuilder } from '@angular/forms';
import { pluck } from 'rxjs/operators';

@Component({
  selector: 'my-app',
  template: `
    

      
      
    
  `
})
export class MyComponent {
  myForm: FormGroup;

  constructor(private fb: FormBuilder) {}

  ngOnInit() {
    this.myForm = this.fb.group({
      firstName: '',
      lastName: ''
    });

    this.myForm.get('firstName').valueChanges.pipe(
      pluck('target', 'value')
    ).subscribe(value => {
      console.log('First name changed to:', value);
    });

    this.myForm.get('lastName').valueChanges.pipe(
      pluck('target', 'value')
    ).subscribe(value => {
      console.log('Last name changed to:', value);
    });
  }
}