Allow removal of specific callbacks from query listeners

Author: Sorowriak

lib/modules/database.js

@@ -211,10 +211,14 @@ class DatabaseRef extends ReferenceBase {
       })
   }
 
-  off(evt='') {
+  off(evt='', origCB) {
     const path = this.dbPath();
-    return this.db.off(path, evt)
+    return this.db.off(path, evt, origCB)
       .then(({callback, subscriptions}) => {
+        if (dbSubscriptions[path][evt].length > 0) {
+          return subscriptions;
+        }
+
         return promisify('off', FirestackDatabase)(path, evt)
           .then(() => {
             // subscriptions.forEach(sub => sub.remove());
@@ -432,15 +436,20 @@ export class Database extends Base {
     return Promise.resolve({callback, subscriptions});
   }
 
-  off(path, evt) {
+  off(path, evt, origCB) {
     const key = this._pathKey(path);
     // Remove subscription
     if (dbSubscriptions[key]) {
       if (!evt || evt === "") {
         dbSubscriptions[key] = {};
       } else if (dbSubscriptions[key][evt]) {
-        delete dbSubscriptions[key][evt];
+        if (origCB) {
+          dbSubscriptions[key][evt].splice(dbSubscriptions[key][evt].indexOf(origCB), 1);
+        } else {
+          delete dbSubscriptions[key][evt];
+        }
       }
+
       if (Object.keys(dbSubscriptions[key]).length <= 0) {
         // there are no more subscriptions
         // so we can unwatch