错误：Can't bind to 'ngModel' since it isn't a known property of 'input' 解决方法：在模块中导入FormsModule，并将其添加到NgModule的imports数组中。

import { FormsModule } from '@angular/forms';

@NgModule({
  imports: [
    FormsModule
  ]
})
export class AppModule { }

错误：ERROR TypeError: Cannot read property 'subscribe' of undefined 解决方法：确保在使用subscribe之前，Observable已经被正确赋值。

import { Component, OnInit } from '@angular/core';
import { Observable } from 'rxjs';

@Component({
  selector: 'app-example',
  template: '...',
})
export class ExampleComponent implements OnInit {
  data$: Observable;

  ngOnInit() {
    this.data$ = this.getData();
    this.data$.subscribe(data => {
      // 处理数据
    });
  }

  getData(): Observable {
    // 返回一个Observable对象
  }
}

错误：Property 'map' does not exist on type 'Observable