Combining arrays using Observables in Typescript with RxJS

Having some issues using rxjs Observable.concat function in typescript. Encountering an error "Cannot read property 'apply' of undefined"

The problem appears to be limited to typescript and may be related to rxjs version 5 concat. The code seems functional with rxjs V4.

Below is a simplified example of the code showcasing the issue...

 /*jshint esnext: true */

console.clear();
console.log('started');
class test{
    observableArray: Observable<any>[]=[];

    constructor(){
        this.observableArray.push(Rx.Observable.return("Line 1"));
        this.observableArray.push(Rx.Observable.return(56));
        this.observableArray.push(Rx.Observable.create((observer)=>{
             setTimeout(()=>{
                try{
                    observer.onNext("Waited for");
                    observer.onCompleted();
                }
                catch(err){
                     observer.onError(err);
                }
             },3000);
         }));
      }

    run(){
         // ... indeterminate number of observables pushed into array.
         // The issue arises below
         var source = Rx.Observable.concat(...this.observableArray);
         // transpiles into js as: source =   Observable_1.Observable.concat.apply(Observable_1.Observable, this.observableArray);
         // Error received in chrome debugger: Cannot read property 'apply' of undefined      

         var subscription = source.subscribe(
             function (x) {
                 console.log('Next: ' + x);
             },
             function (err) {
                 console.error('Error: ' + err);
             },
             function () {
                 console.log('Completed');
         });
      }
  }

}

Check out the live demo on jsbin: https://jsbin.com/naxeba/edit?html,js,console,output

Answer №1

Great news! Issue has been resolved successfully.

Note to all reactive js version 5 users: When using typescript with rxjs, it is important to import each operator individually in order to minimize the application size. Therefore, make sure to add the following line at the beginning of your typescript file for the 'concat' function to work properly:

import {concat} from 'rxjs/operators/concat'

One thing that puzzled me was that I was receiving intellisense suggestions in VS2015 for the Observable.concat function even though I had not imported it.

Answer №2

During my work with rxjs 5.5.7, I came across the need to include

import 'rxjs/add/observable/concat';
.

This is how the code appears:

Observable.concat(...observables).subscribe etc

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