Propagating RTDB type changes

This is a follow-up PR to #840

Author: schmidt-sebastian

packages/database/src/api/DataSnapshot.ts

@@ -133,7 +133,7 @@ export class DataSnapshot {
    * @return {boolean} True if forEach was canceled by action returning true for
    * one of the child nodes.
    */
-  forEach(action: (d: DataSnapshot) => void): boolean {
+  forEach(action: (d: DataSnapshot) => boolean|void): boolean {
     validateArgCount('DataSnapshot.forEach', 1, 1, arguments.length);
     validateCallback('DataSnapshot.forEach', 1, action, false);
 

packages/database/src/core/snap/ChildrenNode.ts

@@ -324,7 +324,7 @@ export class ChildrenNode implements Node {
   /**
    * @inheritDoc
    */
-  forEachChild(index: Index, action: (key: string, node: Node) => void): any {
+  forEachChild(index: Index, action: (key: string, node: Node) => boolean|void): any {
     const idx = this.resolveIndex_(index);
     if (idx) {
       return idx.inorderTraversal(function(wrappedNode) {

packages/firebase/index.d.ts

@@ -428,7 +428,7 @@ declare namespace firebase.database {
     child(path: string): firebase.database.DataSnapshot;
     exists(): boolean;
     exportVal(): any;
-    forEach(action: (a: firebase.database.DataSnapshot) => boolean): boolean;
+    forEach(action: (a: firebase.database.DataSnapshot) => boolean | void): boolean;
     getPriority(): string | number | null;
     hasChild(path: string): boolean;
     hasChildren(): boolean;
@@ -459,6 +459,8 @@ declare namespace firebase.database {
     update(values: Object, onComplete?: (a: Error | null) => any): Promise<any>;
   }
 
+  type EventType = 'value' | 'child_added' | 'child_changed' | 'child_moved' | 'child_removed';
+
   interface Query {
     endAt(
       value: number | string | boolean | null,
@@ -472,22 +474,22 @@ declare namespace firebase.database {
     limitToFirst(limit: number): firebase.database.Query;
     limitToLast(limit: number): firebase.database.Query;
     off(
-      eventType?: string,
+      eventType?: EventType,
       callback?: (a: firebase.database.DataSnapshot, b?: string | null) => any,
       context?: Object | null
     ): any;
     on(
-      eventType: string,
+      eventType: EventType,
       callback: (a: firebase.database.DataSnapshot | null, b?: string) => any,
       cancelCallbackOrContext?: Object | null,
       context?: Object | null
     ): (a: firebase.database.DataSnapshot | null, b?: string) => any;
     once(
-      eventType: string,
+      eventType: EventType,
       successCallback?: (a: firebase.database.DataSnapshot, b?: string) => any,
       failureCallbackOrContext?: Object | null,
       context?: Object | null
-    ): Promise<any>;
+    ): Promise<DataSnapshot>;
     orderByChild(path: string): firebase.database.Query;
     orderByKey(): firebase.database.Query;
     orderByPriority(): firebase.database.Query;