feat(callback): Add Observable.fromCallback

spec/observables/from-callback-spec.js

@@ -0,0 +1,97 @@
+/* globals describe, it, expect */
+var Rx = require('../../dist/cjs/Rx');
+var Observable = Rx.Observable;
+
+describe('Observable.fromCallback', function () {
+  it('should emit one value from a callback', function (done) {
+    function callback (datum, cb) {
+      cb(datum);
+    }
+    var cbToObs = Observable.fromCallback(callback);
+
+    cbToObs(42)
+      .subscribe(function (x) {
+        expect(x).toBe(42);
+      }, function () {
+        done.fail('should not be called');
+      },
+      done);
+  });
+
+  it('should emit one value chosen by a selector', function (done) {
+    function callback (datum, cb) {
+      cb(null, datum);
+    }
+    var cbToObs = Observable.fromCallback(callback, null, function (err, datum) { return datum; });
+
+    cbToObs(42)
+      .subscribe(function (x) {
+        expect(x).toBe(42);
+      }, function () {
+        done.fail('should not be called');
+      },
+      done);
+  });
+
+  it('should override `this` in the callback', function (done) {
+    function callback (cb) {
+      cb(this.value);
+    }
+    var cbToObs = Observable.fromCallback(callback, {value: 42});
+
+    cbToObs()
+      .subscribe(function (x) {
+        expect(x).toBe(42);
+      }, function () {
+        done.fail('should not be called');
+      },
+      done);
+  });
+
+  it('should emit an error when the selector throws', function (done) {
+    function callback (cb) {
+      cb(42);
+    }
+    var cbToObs = Observable.fromCallback(callback, null, function (err) { throw new Error('Yikes!'); });
+
+    cbToObs()
+      .subscribe(function () {
+        // Considered a failure if we don't go directly to err handler
+        done.fail('should not be called');
+      },
+      function (err) {
+        expect(err.message).toBe('Yikes!');
+        done();
+      },
+      function () {
+        // Considered a failure if we don't go directly to err handler
+        done.fail('should not be called');
+      }
+      );
+  });
+
+  it('should not emit, throw or complete if immediately unsubscribed', function (done) {
+    var nextSpy = jasmine.createSpy('next');
+    var throwSpy = jasmine.createSpy('throw');
+    var completeSpy = jasmine.createSpy('complete');
+    var timeout;
+    function callback (datum, cb) {
+      // Need to cb async in order for the unsub to trigger
+      timeout = setTimeout(function () {
+        cb(datum);
+      });
+    }
+    var subscription = Observable.fromCallback(callback)(42)
+      .subscribe(nextSpy, throwSpy, completeSpy);
+    subscription.unsubscribe();
+
+    setTimeout(function () {
+      expect(nextSpy).not.toHaveBeenCalled();
+      expect(throwSpy).not.toHaveBeenCalled();
+      expect(completeSpy).not.toHaveBeenCalled();
+
+      clearTimeout(timeout);
+      done();
+    });
+  });
+});

src/Observable.ts

@@ -149,6 +149,7 @@ export class Observable<T> implements CoreOperators<T>  {
                                removeHandler: (handler: Function) => void,
                                selector?: (...args: Array<any>) => T) => Observable<T>;
   static fromPromise: <T>(promise: Promise<T>, scheduler?: Scheduler) => Observable<T>;
+  static fromCallback: <T>(callbackFunc: Function, ctx?: Object, selector?: Function, scheduler?: Scheduler) => Function;
   static interval: (interval: number, scheduler?: Scheduler) => Observable<number>;
   static merge: <T>(...observables: Array<Observable<any> | Scheduler | number>) => Observable<T>;
   static never: <T>() => Observable<T>;

src/Rx.KitchenSink.ts

@@ -53,6 +53,9 @@ Observable.fromEventPattern = FromEventPatternObservable.create;
 import {PromiseObservable} from './observables/PromiseObservable';
 Observable.fromPromise = PromiseObservable.create;
 
+import {CallbackObservable} from './observables/CallbackObservable';
+Observable.fromCallback = CallbackObservable.create;
+
 import {IntervalObservable} from './observables/IntervalObservable';
 Observable.interval = IntervalObservable.create;
 

src/Rx.ts

@@ -36,6 +36,9 @@ Observable.fromEventPattern = FromEventPatternObservable.create;
 import {PromiseObservable} from './observables/PromiseObservable';
 Observable.fromPromise = PromiseObservable.create;
 
+import {CallbackObservable} from './observables/CallbackObservable';
+Observable.fromCallback = CallbackObservable.create;
+
 import {IntervalObservable} from './observables/IntervalObservable';
 Observable.interval = IntervalObservable.create;
 

src/observables/CallbackObservable.ts

@@ -0,0 +1,110 @@
+import {Observable} from '../Observable';
+import {Subscriber} from '../Subscriber';
+import {Scheduler} from '../Scheduler';
+import {Subscription} from '../Subscription';
+import {immediate} from '../schedulers/immediate';
+import {tryCatch} from '../util/tryCatch';
+import {errorObject} from '../util/errorObject';
+
+export class CallbackObservable<T> extends Observable<T> {
+
+  _isScalar: boolean = false;
+  value: T | T[];
+
+  static create<T>(callbackFunc: Function,
+                   ctx: Object = undefined,
+                   selector: Function = undefined,
+                   scheduler: Scheduler = immediate): Function {
+    return (...args): Observable<T> => {
+      return new CallbackObservable(callbackFunc, ctx, selector, args, scheduler);
+    };
+  }
+
+  constructor(private callbackFunc: Function,
+              private ctx,
+              private selector,
+              private args: any[],
+              public scheduler: Scheduler = immediate) {
+    super();
+  }
+
+  _subscribe(subscriber: Subscriber<T | T[]>) {
+    const callbackFunc = this.callbackFunc;
+    const ctx = this.ctx;
+    const selector = this.selector;
+    const args = this.args;
+    const scheduler = this.scheduler;
+
+    let handler;
+
+    if (scheduler === immediate) {
+      if (this._isScalar) {
+        subscriber.next(this.value);
+        subscriber.complete();
+      } else {
+        handler = (...innerArgs) => {
+          let results;
+
+          this._isScalar = true;
+          this.value = innerArgs;
+
+          if (selector) {
+            results = tryCatch(selector).apply(ctx, innerArgs);
+            if (results === errorObject) { return subscriber.error(results.e); }
+            subscriber.next(results);
+          } else {
+            if (innerArgs.length <= 1) {
+              subscriber.next(innerArgs[0]);
+            } else {
+              subscriber.next(innerArgs);
+            }
+          }
+          subscriber.complete();
+        };
+      }
+    } else {
+      const subscription = new Subscription();
+      if (this._isScalar) {
+        const value = this.value;
+        subscription.add(scheduler.schedule(dispatchNext, 0, { value, subscriber }));
+      } else {
+        handler = (...innerArgs) => {
+          let results;
+
+          this._isScalar = true;
+
+          if (selector) {
+            results = tryCatch(selector).apply(ctx, innerArgs);
+            if (results === errorObject) {
+              return subscription.add(scheduler.schedule(dispatchError, 0, { err: results.e, subscriber }));
+            }
+            this.value = results;
+          } else {
+            if (innerArgs.length <= 1) {
+              this.value = innerArgs[0];
+            } else {
+              this.value = innerArgs;
+            }
+          }
+          const value = this.value;
+          subscription.add(scheduler.schedule(dispatchNext, 0, { value, subscriber }));
+        };
+        return subscription;
+      }
+    }
+
+    if (handler) {
+      args.push(handler);
+      callbackFunc.apply(ctx, args);
+    }
+  }
+}
+
+function dispatchNext({ value, subscriber }) {
+  subscriber.next(value);
+  subscriber.complete();
+}
+
+function dispatchError({ err, subscriber }) {
+  subscriber.error(err);
+}