Cleaner handling chain.

lib/modules/database/index.js

@@ -159,25 +159,12 @@ export default class Database extends Base {
     FirestackDatabase.goOffline();
   }
 
-  addTransaction(path, updateCallback, applyLocally, onComplete) {
+  addTransaction(path, updateCallback, applyLocally) {
     let id = this._generateTransactionID();
     this.transactions[id] = updateCallback;
-    return new Promise((resolve, reject) => {
-      FirestackDatabase.beginTransaction(path, id, applyLocally || false, (error, result) => {
-        let snapshot;
-        if (result.snapshot)
-          snapshot = new Snapshot(new Reference(this, path.split('/'), null), result.snapshot);
-        onComplete && onComplete(error, snapshot);
-        if (error) {
-          reject(error);
-        }
-        else {
-          let {committed} = result;
-          resolve({committed, snapshot});
-        }
-        delete this.transactions[id];
-      });  
-    });
+    return promisify('beginTransaction', FirestackDatabase)(path, id, applyLocally || false)
+      .then((v) => {delete this.transactions[id]; return v;},
+            (e) => {delete this.transactions[id]; throw e;}); 
   }
 
   _generateTransactionID() {

lib/modules/database/reference.js

@@ -125,7 +125,15 @@ export default class Reference extends ReferenceBase {
 
   transaction(transactionUpdate, onComplete, applyLocally) {
     const path = this._dbPath();
-    return this.db.addTransaction(path, transactionUpdate, applyLocally, onComplete);
+    return this.db.addTransaction(path, transactionUpdate, applyLocally)
+      .then(({ snapshot, committed }) => {snapshot: new Snapshot(this, snapshot), committed})
+      .then(({ snapshot, committed }) => {
+        if (isFunction(onComplete)) onComplete(null, snapshot);
+        return {snapshot, committed};
+      }).catch((e) => {
+        if (isFunction(onComplete)) return onComplete(e, null);
+        throw e;
+      });
   }
 
   /**