Sequential angular 4 get call

Question

My application, at the start, needs to get the list of the links so at the beginning I call the principal endpoint to get this list and I store it into a Map.

Now for example if a user call directly the products page, my application needs to do 2 Get call sequentially, first Get call the principal endpoint and store all the links in a Map, then the second Get call the respective product link from the Map.

So what is the best practice in angular to synchronize those 2 calls? (making the second call only after the result of the first one.)

======================================================================== Update

 public getLinks2(modelName: string, searchMap: Map<string, string>) {

    return this.http.get(EndpointUrlService.baseUrl)
      // Prima popolo la mia mappa con la response quindi con tutti i link
      .map((response: any) => {
        this.linksMap = response._links;
        (<any>Object).entries(this.linksMap).forEach(
          ([key, value]) => {
            this.map.set(key, value.href);
          }
        )
      })
      .flatMap((res) => {
        return this.http.get(this.cutLinks(this.map.get(modelName)) + '/search')
      })
      .map((response: any) => {
        console.log(response);
        (<any>Object).entries(response._links).forEach(
          ([key, value]) => {
            searchMap.set(key, value.href);
          }
        )
      })
  }

So this is my method implemented with flatMap operator, in this case with first Get call I retrieve all the links from the principal endpoint and I store this list in a Map, then with flatMap I call the desidered endpoint (modelName) from saved Map to retrieve the Search link desidered and I store it in other Map (searchMap)

At the end in my component I call one of the search links stored in searchMap:

this.endPointUrlService.getLinks2(this.getModelName(), this.endPointUrlService.mapNames.get(this.searchMapName()))
        .subscribe((res) => {
          this.loadModelData(event)
        });

It is a good practice? it seems works well