Angular 2: How to call a function after get a response from subscribe http.post

Update your get_categories() method to return the total (wrapped in an observable):

// Note that .subscribe() is gone and I've added a return.get_categories(number) {  return this.http.post( url, body, {headers: headers, withCredentials:true})    .map(response => response.json());}

In search_categories(), you can subscribe the observable returned by get_categories() (or you could keep transforming it by chaining more RxJS operators):

// send_categories() is now called after get_categories().search_categories() {  this.get_categories(1)    // The .subscribe() method accepts 3 callbacks    .subscribe(      // The 1st callback handles the data emitted by the observable.      // In your case, it's the JSON data extracted from the response.      // That's where you'll find your total property.      (jsonData) => {        this.send_categories(jsonData.total);      },      // The 2nd callback handles errors.      (err) => console.error(err),      // The 3rd callback handles the "complete" event.      () => console.log("observable complete")    );}

Note that you only subscribe ONCE, at the end.

Like I said in the comments, the .subscribe() method of any observable accepts 3 callbacks like this:

obs.subscribe(  nextCallback,  errorCallback,  completeCallback);

They must be passed in this order. You don't have to pass all three. Many times only the nextCallback is implemented:

obs.subscribe(nextCallback);

You can add a callback function to your list of get_category(...) parameters.

Ex:

 get_categories(number, callback){ this.http.post( url, body, {headers: headers, withCredentials:true})    .subscribe(       response => {        this.total = response.json();        callback();       }, error => {    }  ); }

And then you can just call get_category(...) like this:

this.get_category(1, name_of_function);

You can code as a lambda expression as the third parameter(on complete) to the subscribe method. Here I re-set the departmentModel variable to the default values.

saveData(data:DepartmentModel){  return this.ds.sendDepartmentOnSubmit(data).  subscribe(response=>this.status=response,   ()=>{},   ()=>this.departmentModel={DepartmentId:0});}