fix(FirebaseListFactory): prevent first item being duplicated when it changes (angular#140)

Author: rosslavery

src/utils/firebase_list_factory.spec.ts

@@ -169,6 +169,11 @@ describe('FirebaseListFactory', () => {
         ).toEqual([val2, val1, val3]);
       });
 
+      it('should not duplicate the first item if it is the one that changed', () => {
+        expect(
+          onChildChanged([val1, val2, val3], val1, null)
+        ).not.toEqual([val1, val1, val2, val3]);
+      });
 
       it('should not mutate the input array', () => {
         var inputArr = [val1, val2];

src/utils/firebase_list_factory.ts

@@ -94,7 +94,9 @@ export function onChildChanged(arr:any[], child:any, prevKey:string): any[] {
   return arr.reduce((accumulator:any[], val:any, i:number) => {
     if (!prevKey && i==0) {
       accumulator.push(child);
-      accumulator.push(val);
+      if (val.key() !== child.key()) {
+        accumulator.push(val);
+      }
     } else if(val.key() === prevKey) {
       accumulator.push(val);
       accumulator.push(child);