fix(partition): handles thisArg as expected (#2138)

This fix ensures that the `partition` will call `predicate` with`thisArg` as expected if it is specified.

spec/operators/partition-spec.ts

@@ -39,6 +39,20 @@ describe('Observable.prototype.partition', () => {
     expectSubscriptions(e1.subscriptions).toBe([e1subs, e1subs]);
   });
 
+  it('should partition an observable into two using a predicate and thisArg', () => {
+    const e1 =    hot('--a-b---a------d--a---c--|');
+    const e1subs =    '^                        !';
+    const expected = ['--a-----a---------a------|',
+                    '----b----------d------c--|'];
+
+    function predicate(x) {
+      return x === this.value;
+    }
+
+    expectObservableArray(e1.partition(predicate, {value: 'a'}), expected);
+    expectSubscriptions(e1.subscriptions).toBe([e1subs, e1subs]);
+  });
+
   it('should pass errors to both returned observables', () => {
     const e1 =    hot('--a-b---#');
     const e1subs =    '^       !';
@@ -225,4 +239,14 @@ describe('Observable.prototype.partition', () => {
     const e1 = hot('--a-b---a------d----');
     expect(e1.partition).to.throw();
   });
+
+  it('should accept thisArg', () => {
+    const thisArg = {};
+
+    Observable.of(1).partition(function (value: number) {
+      expect(this).to.deep.equal(thisArg);
+      return true;
+    }, thisArg)
+      .forEach((observable: Rx.Observable<number>) => observable.subscribe());
+  });
 });

src/operator/partition.ts

@@ -45,7 +45,7 @@ import { Observable } from '../Observable';
  */
 export function partition<T>(this: Observable<T>, predicate: (value: T) => boolean, thisArg?: any): [Observable<T>, Observable<T>] {
   return [
-    filter.call(this, predicate),
+    filter.call(this, predicate, thisArg),
     filter.call(this, not(predicate, thisArg))
   ];
 }