fix(errors): Better error message when you return non-observable thin…

…gs, (#2152)

like `undefined`

fixes #215

spec/util/subscribeToResult-spec.ts

@@ -125,7 +125,8 @@ describe('subscribeToResult', () => {
  const subscriber = new OuterSubscriber(x => {
  done(new Error('should not be called'));
  }, (x) => {
- expect(x).to.be.an('error', 'invalid observable');
+ expect(x).to.be.an('error');
+ expect(x.message).to.be.equal('Provided object does not correctly implement Symbol.observable');
  done();
  }, () => {
  done(new Error('should not be called'));
@@ -138,12 +139,31 @@ describe('subscribeToResult', () => {
  const subscriber = new OuterSubscriber(x => {
  done(new Error('should not be called'));
  }, (x) => {
- expect(x).to.be.an('error', 'unknown type returned');
+ expect(x).to.be.an('error');
+ const msg = 'You provided an invalid object where a stream was expected.'
+ + ' You can provide an Observable, Promise, Array, or Iterable.';
+ expect(x.message).to.be.equal(msg);
  done();
  }, () => {
  done(new Error('should not be called'));
  });
 
  subscribeToResult(subscriber, {});
  });
+
+ it('should emit an error when trying to subscribe to a non-object', (done: MochaDone) => {
+ const subscriber = new OuterSubscriber(x => {
+ done(new Error('should not be called'));
+ }, (x) => {
+ expect(x).to.be.an('error');
+ const msg = 'You provided \'null\' where a stream was expected.'
+ + ' You can provide an Observable, Promise, Array, or Iterable.';
+ expect(x.message).to.be.equal(msg);
+ done();
+ }, () => {
+ done(new Error('should not be called'));
+ });
+
+ subscribeToResult(subscriber, null);
+ });
 });

src/util/subscribeToResult.ts

@@ -1,6 +1,7 @@
 import { root } from './root';
 import { isArray } from './isArray';
 import { isPromise } from './isPromise';
+import { isObject } from './isObject';
 import { Subscriber } from '../Subscriber';
 import { Observable, ObservableInput } from '../Observable';
 import { $$iterator } from '../symbol/iterator';
@@ -31,9 +32,7 @@ export function subscribeToResult<T>(outerSubscriber: OuterSubscriber<any, any>,
  } else {
  return result.subscribe(destination);
  }
- }
-
- if (isArray(result)) {
+ } else if (isArray(result)) {
  for (let i = 0, len = result.length; i < len && !destination.closed; i++) {
  destination.next(result[i]);
  }
@@ -55,7 +54,7 @@ export function subscribeToResult<T>(outerSubscriber: OuterSubscriber<any, any>,
  root.setTimeout(() => { throw err; });
  });
  return destination;
- } else if (typeof result[$$iterator] === 'function') {
+ } else if (result && typeof result[$$iterator] === 'function') {
  const iterator = <any>result[$$iterator]();
  do {
  let item = iterator.next();
@@ -68,15 +67,18 @@ export function subscribeToResult<T>(outerSubscriber: OuterSubscriber<any, any>,
  break;
  }
  } while (true);
- } else if (typeof result[$$observable] === 'function') {
+ } else if (result && typeof result[$$observable] === 'function') {
  const obs = result[$$observable]();
  if (typeof obs.subscribe !== 'function') {
- destination.error(new Error('invalid observable'));
+ destination.error(new TypeError('Provided object does not correctly implement Symbol.observable'));
  } else {
  return obs.subscribe(new InnerSubscriber(outerSubscriber, outerValue, outerIndex));
  }
  } else {
- destination.error(new TypeError('unknown type returned'));
+ const value = isObject(result) ? 'an invalid object' : `'${result}'`;
+ const msg = `You provided ${value} where a stream was expected.`
+ + ' You can provide an Observable, Promise, Array, or Iterable.';
+ destination.error(new TypeError(msg));
  }
  return null;
 }