Coding Challenge Practice - Question 74

The task is implement map(), as the name indicates, it maps the value to another value thus creating a new event stream.

The boilerplate code

function map(transform) {
  // your code here
}

Think of map as a machine that sits between original event stream and new event stream. It takes a transform function and returns a new observable.

  return (sourceObservable) =>
    new Observable((observer) => { 
   }
}

When the new observable is subscribed to, it subscribes to the original observable. Every time the original observable sends a value, the value is transformed and set to the new observable.

return sourceObservable.subscribe({
        next(value) {
          observer.next(transform(value));
        },

Errors and completion are passed through unchanged

error(err) {
          observer.error(err);
        },
        complete() {
          observer.complete();
        }

So map doesn't change the original stream, it creates a new stream where each emitted value is transformed.

The final code

function map(transform) {
  // your code here
   return (sourceObservable) =>
    new Observable((observer) => {
      return sourceObservable.subscribe({
        next(value) {
          observer.next(transform(value));
        },
        error(err) {
          observer.error(err);
        },
        complete() {
          observer.complete();
        }
      });
    });
}

That's all folks!