feat(BehaviorSubject): add getValue method to access value

- adds `getValue` method to get inner value
- further hides the value as `_value`
- adds `value` property getter
- purposefully excludes `value` property setter
- adds tests around `getValue` method and `value` property

fixes #758

spec/subjects/behavior-subject-spec.js

@@ -12,6 +12,29 @@ describe('BehaviorSubject', function () {
     done();
   });
 
+  it('should have a getValue() method to retrieve the current value', function () {
+    var subject = new BehaviorSubject('staltz');
+    expect(subject.getValue()).toBe('staltz');
+
+    subject.next('oj');
+
+    expect(subject.getValue()).toBe('oj');
+  });
+
+  it('should not allow you to set `value` directly', function () {
+    var subject = new BehaviorSubject('flibberty');
+    subject.value = 'jibbets';
+    expect(subject.getValue()).toBe('flibberty');
+    expect(subject.value).toBe('flibberty');
+  });
+
+  it('should still allow you to retrieve the value from the value property', function () {
+    var subject = new BehaviorSubject('fuzzy');
+    expect(subject.value).toBe('fuzzy');
+    subject.next('bunny');
+    expect(subject.value).toBe('bunny');
+  });
+
   it('should start with an initialization value', function (done) {
     var subject = new BehaviorSubject('foo');
     var expected = ['foo', 'bar'];

src/subject/BehaviorSubject.ts

@@ -3,21 +3,29 @@ import {Subscriber} from '../Subscriber';
 import {Subscription} from '../Subscription';
 
 export class BehaviorSubject<T> extends Subject<T> {
-  constructor(private value: any) {
+  constructor(private _value: T) {
     super();
   }
 
+  getValue(): T {
+    return this._value;
+  }
+
+  get value(): T {
+    return this._value;
+  }
+
   _subscribe(subscriber: Subscriber<any>): Subscription<T> {
     const subscription = super._subscribe(subscriber);
     if (!subscription) {
       return;
     } else if (!subscription.isUnsubscribed) {
-      subscriber.next(this.value);
+      subscriber.next(this._value);
     }
     return subscription;
   }
 
   _next(value: T): void {
-    super._next(this.value = value);
+    super._next(this._value = value);
   }
 }