angular2 2异步调用

Question

Angular2, typescript

I have a component that displays 1 object at a time from the server.

On the click of a button, the form does some action on the object, sends data to the server. Immediately in the next line, the next object is got.

this.rawS.updateTags({......}); //Update object
this.candidateC.footerNavigateTo(.....);//Get next object

But there is a race condition where ajax to get next object reaches the server before the updateTags ajax reaches the server.

Code of updateTags is

  updateTags(rawCandidate) {
    this.baseAjaxService.doPost(this.baseUrl + 'tags/update', rawCandidate)
      .subscribe(data => {
        console.log(data);
      });
  }

Code for doPost is

doPost(url, inputParamJSON){
    let httpResponse  = this.http
      .post(url, inputParamJSON, this.options)
      .map(this.extractData)
      .catch(this.handleAjaxError);
    return httpResponse;
}

The route for 'continue_screening' has a route resolver which brings the next object.

How can I ensure that footerNavigateTo() runs only after updateTags has completed its full cycle?

Answer 1

If what you want is to have different behaviours depending on where the function updateTags(rawCandidate) is called, I propose the following solution:

  updateTags(rawCandidate, action) {
    this.baseAjaxService.doPost(this.baseUrl + 'tags/update', rawCandidate)
      .subscribe(
       data => {
        action(data);

      },
      error => {
          console.log("error"); //handle error here
      });
  }

Then you can call the function like this:

updateTags(rawCandidate, function(data){
   console.log(data);
   this.candidateC.footerNavigateTo(.....);//here you can use data
});

Answer 2

What you want to achieve here is to chain your two http calls, make them dependents somehow. In Angular 1.X it would be done using promise but with AngularJS 2 you can achieve that using flatMap .

See this link http://www.syntaxsuccess.com/viewarticle/angular-2.0-and-http at Dependent calls section.

PS : As indicated in this post ( Combining promises in Angular 2 ) you can also use toPromise() to transform your Observable (ie your async http call) into a Promise, if you are more familiar with it.