How to create an Observable from static data similar to http one in Angular

Question

I am having a service that has this method   export class TestModelService        public testModel  TestModel       constructor   Inject Http  public http  Http               public fetchModel uuid  string   undefined   Observable lt string gt            if  uuid                  return Observable of JSON stringify new TestModel                       else               return this http get  http   localhost 8080 myapp api model     uuid                   map res   gt  res text                         in the component s constructor I am subscribing like this   export class MyComponent      testModel  TestModel     testModelService  TestModelService      constructor  Inject TestModelService  testModelService          this testModelService   testModelService         testService fetchModel  29f4fddc-155a-4f26-9db6-5a431ecd5d44   subscribe            data   gt    this testModel   FactModel fromJson JSON parse data                 err   gt  console log err                    This works if an object comes from the server but I am trying to create an observable that will work with the given subscribe   call for a static string  this happens when testModelService fetchModel   does not receive an uuid  so there is seamless handling in both cases

User · Answer

Things seem to have changed since Angular 2.0.0

import { Observable } from 'rxjs/Observable';
import { Subscriber } from 'rxjs/Subscriber';
// ...
public fetchModel(uuid: string = undefined): Observable<string> {
  if(!uuid) {
    return new Observable<TestModel>((subscriber: Subscriber<TestModel>) => subscriber.next(new TestModel())).map(o => JSON.stringify(o));
  }
  else {
    return this.http.get("http://localhost:8080/myapp/api/model/" + uuid)
            .map(res => res.text());
  }
}

The .next() function will be called on your subscriber.

User · Answer

This is how you can create a simple observable for static data   let observable   Observable create observer   gt      setTimeout      gt        let users            username  balwant padwal  city  pune           username  test  city  mumbai         observer next users      This method same as resolve   method from Angular 1     console log  am done        observer complete     to show we are done with our processing        observer error new Error  error message          2000        to subscribe to it is very easy  observable subscribe  data   gt     console log data      users array display       I hope this answer is helpful  We can use HTTP call instead static data

User · Answer

This way you can create Observable from data  in my case I need to maintain shopping cart   service ts  export class OrderService       cartItems  BehaviorSubject lt Array lt any gt  gt    new BehaviorSubject          cartItems    this cartItems asObservable            I need to maintain cart  so add items in cart      addCartData data            const currentValue   this cartItems value     get current items in cart         const updatedValue       currentValue  data      push new item in cart          if updatedValue length              this cartItems next updatedValue      notify to all subscribers                       Component ts  export class CartViewComponent implements OnInit       cartProductList  any           constructor          private order  OrderService                ngOnInit             this order cartItems  subscribe items   gt                this cartProductList   items

User · Answer

As of July 2018 and the release of RxJS 6  the new way to get an Observable from a value is to import the of operator like so  import   of   from  rxjs    and then create the observable from the value  like so  of someValue    Note  that you used to have to do Observable of someValue  like in the currently accepted answer  There is a good article on the other RxJS 6 changes here

User · Answer

Perhaps you could try to use the of method of the Observable class   import   Observable   from  rxjs Observable   import  rxjs add observable of    public fetchModel uuid  string   undefined   Observable lt string gt      if  uuid        return Observable of new TestModel    map o   gt  JSON stringify o          else       return this http get  http   localhost 8080 myapp api model     uuid               map res   gt  res text

[typescript] How to create an Observable from static data similar to http one in Angular?

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