Chaining promises in TypeScript - Angular 2

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Chaining promises in TypeScript - Angular 2

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#1 by (1 votes)

1

I have an application that consumes a REST API. With a GET I get a JSON and within that JSON there are several URLs with which I also do GET. For the purpose of the application I have to be careful with the synchronization (hence I use promises). How can I pass the URLs of the first JSON to the second promise to access them there?

this.http.get(data.jobs[i].url + this.finalURL).subscribe(
    response => {
    let data2 = response.json();
    let numberOfFails: number = 0;
    var init;
    if (data2.builds.length < 10){
       init = data2.builds.length-1;
    } else {
       init = 9;
    }
    for (var j = init; j >= 0; j--){
       console.log("Iteracion " + j + " numberOfFails " + numberOfFails);
       this.http.get(data2.builds[j].url + this.finalURL).subscribe(response => {
       let data3 = response.json();
       console.log(data3);
       if(data3.result == "FAILURE"){
          numberOfFails = numberOfFails+1;
       }
       }, error => console.error(error));
    }

And what has been said, some synchronization is necessary because it is possible that it continues without solving all the GET requests making, for example, numberOfFails can vary.

typescript angularjs-2.0 promesas http

asked by Carlos Y 26.05.2017 в 00:58

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1 answer

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score 1 · Answer 1

The call to this.http.get(...) does not return a promise, but an Observable, which is a different concept .

Among the operations that we can perform with observables is map , which allows creating a new observable with the transformation of the first results:

Therefore the solution to what you want could be the following:

let urlStream = this.http.get(data.jobs[i].url + this.finalURL)
  .map((res: Response) => {
    let data2 = response.json();
    let numberOfFails: number = 0;
    var init;
    if (data2.builds.length < 10){
       init = data2.builds.length-1;
    } else {
       init = 9;
    }
    let urls=[];
    for (var j = init; j >= 0; j--){
      urls.push(data2.builds[j].url + this.finalURL);
    }
    return Observable.from(urls); //convierte el array en un stream
  });

  urlStream.observe((url) =>{
     //el parámetro url es cada uno de las URL generadas arriba,
     //esta función se podrá ejecutar hasta 10 veces, porque hemos 
     //generado un máximo de 10 URLs
  }