Coding Challenge Practice - Question 74

Source: Dev.to

Description

The map() operator creates a new observable by applying a transformation function to each value emitted by the original (source) observable. It does not modify the source stream; instead, it produces a new stream where every emitted value is the result of transform(value). Errors and completion notifications are passed through unchanged.

Implementation

function map(transform) {
  // Returns a function that takes the source observable
  // and returns a new observable applying the transformation.
  return (sourceObservable) =>
    new Observable((observer) => {
      // Subscribe to the source observable
      return sourceObservable.subscribe({
        // Transform each emitted value
        next(value) {
          observer.next(transform(value));
        },
        // Forward errors unchanged
        error(err) {
          observer.error(err);
        },
        // Forward completion unchanged
        complete() {
          observer.complete();
        }
      });
    });
}