@Yukko wrote:
Hey guys,
i’m fairly new to observables and i’m currently trying to change some code to understand the concept as a whole.
However, i came across a problem. I want to access my API using the http observable.return this.http.get(BACKEND_URL + '/api/ROUTE', { headers: headers, params: params, observe: 'response' }).pipe(map(response => { this.localStorage.setEtag(response.headers.get('etag')); }));Before that, i want to add a header containing the last etag, which will get saved into local storage after fetching the data.
llet headers = new HttpHeaders() .append('accept-language', localLanguage); if (etag != null) headers = headers.append('If-None-Match', etag);Now my problem lies within receiving the saved etag and waiting for it, since it is asynchonous.
let etag = ''; this.localStorage.getEtag() .then(data => { etag = data; });How can i wait for the local storage to complete in order to actually append it to the headers? The local storage returns as far as i know a promise of the value. For that reason i would like to (And had it prior to the observables) that i just
awaitthe etag and then append it into the headers. However, since this new method returns the observable i can’t await it since it would turn the return type to a promise.
I don’t know, if this whole approach is wrong at its core, i would appreciate some help.Here is the full request method:
public getInstances(): Observable<any> { let etag = ''; this.localStorage.getEtagInstances() .then(data => { etag = data; }); let headers = new HttpHeaders() .append('accept-language', localLanguage); if (etag != null) headers = headers.append('If-None-Match', etag); return this.http.get(BACKEND_URL + '/api/ROUTE', { headers: headers, params: params, observe: 'response' }).pipe(map(response => { this.localStorage.setEtagInstances(response.headers.get('etag')) })) }
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