How to create an Observable from static data similar to http one in Angular?
TypescriptPromiseAngularObservableRxjsTypescript Problem Overview
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<string> {
if(!uuid) {
//return Observable of JSON.stringify(new TestModel());
}
else {
return this.http.get("http://localhost:8080/myapp/api/model/" + uuid)
.map(res => 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 => { this.testModel = FactModel.fromJson(JSON.parse(data)); },
err => 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.
Typescript Solutions
Solution 1 - Typescript
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<string> {
if(!uuid) {
return Observable.of(new TestModel()).map(o => JSON.stringify(o));
}
else {
return this.http.get("http://localhost:8080/myapp/api/model/" + uuid)
.map(res => res.text());
}
}
Solution 2 - Typescript
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.
Solution 3 - Typescript
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.
Solution 4 - Typescript
This is how you can create a simple observable for static data.
let observable = Observable.create(observer => {
setTimeout(() => {
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)=>{
console.log(data); // users array display
});
I hope this answer is helpful. We can use HTTP call instead static data.
Solution 5 - Typescript
This way you can create Observable from data, in my case I need to maintain shopping cart:
service.ts
export class OrderService {
cartItems: BehaviorSubject<Array<any>> = 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 => {
this.cartProductList = items;
});
}
}
Solution 6 - Typescript
As of May 2021 the new way to get an Observable from a value is:
importing:
import "rxjs/add/observable/of"
import { Observable } from "rxjs/Observable"
and using, like so::
Observable.of(your_value)