例子
import { Component, OnInit } from '@angular/core';
import { FormBuilder, FormGroup, Validators, FormControl..., AbstractControl } from '@angular/forms';
import { concat, merge, zip, combineLatest, race } from 'rxjs...(
private formBuilder: FormBuilder,
) { }
ngOnInit() {
this.form = this.formBuilder.group...,只需要在pipe添加相应的运算符。...').pipe(startWith(this.form.get('hobby').value))
// combineLatest,它会取得各个 observable 最后送出的值,再输出成一个值