Factor createMatrixClient out from MatrixClientPeg

... so that it can be used elsewhere.

src/MatrixClientPeg.js

@@ -16,12 +16,10 @@ limitations under the License.
 
 'use strict';
 
-import Matrix from 'matrix-js-sdk';
 import utils from 'matrix-js-sdk/lib/utils';
 import EventTimeline from 'matrix-js-sdk/lib/models/event-timeline';
 import EventTimelineSet from 'matrix-js-sdk/lib/models/event-timeline-set';
-
-const localStorage = window.localStorage;
+import createMatrixClient from './utils/createMatrixClient';
 
 interface MatrixClientCreds {
     homeserverUrl: string,
@@ -129,22 +127,7 @@ class MatrixClientPeg {
             timelineSupport: true,
         };
 
-        if (localStorage) {
-            opts.sessionStore = new Matrix.WebStorageSessionStore(localStorage);
-        }
-        if (window.indexedDB && localStorage) {
-            // FIXME: bodge to remove old database. Remove this after a few weeks.
-            window.indexedDB.deleteDatabase("matrix-js-sdk:default");
-
-            opts.store = new Matrix.IndexedDBStore({
-                indexedDB: window.indexedDB,
-                dbName: "riot-web-sync",
-                localStorage: localStorage,
-                workerScript: this.indexedDbWorkerScript,
-            });
-        }
-
-        this.matrixClient = Matrix.createClient(opts);
+        this.matrixClient = createMatrixClient(opts);
 
         // we're going to add eventlisteners for each matrix event tile, so the
         // potential number of event listeners is quite high.

src/utils/createMatrixClient.js

@@ -0,0 +1,55 @@
+/*
+Copyright 2017 Vector Creations Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import Matrix from 'matrix-js-sdk';
+
+const localStorage = window.localStorage;
+
+/**
+ * Create a new matrix client, with the persistent stores set up appropriately
+ * (using localstorage/indexeddb, etc)
+ *
+ * @param {Object} opts  options to pass to Matrix.createClient. This will be
+ *    extended with `sessionStore` and `store` members.
+ *
+ * @param {string} indexedDbWorkerScript  Optional URL for a web worker script
+ *    for IndexedDB store operations. If not given, indexeddb ops are done on
+ *    the main thread.
+ *
+ * @returns {MatrixClient} the newly-created MatrixClient
+ */
+export default function createMatrixClient(opts, indexedDbWorkerScript) {
+    const storeOpts = {};
+
+    if (localStorage) {
+        storeOpts.sessionStore = new Matrix.WebStorageSessionStore(localStorage);
+    }
+    if (window.indexedDB && localStorage) {
+        // FIXME: bodge to remove old database. Remove this after a few weeks.
+        window.indexedDB.deleteDatabase("matrix-js-sdk:default");
+
+        storeOpts.store = new Matrix.IndexedDBStore({
+            indexedDB: window.indexedDB,
+            dbName: "riot-web-sync",
+            localStorage: localStorage,
+            workerScript: indexedDbWorkerScript,
+        });
+    }
+
+    opts = Object.assign(storeOpts, opts);
+
+    return Matrix.createClient(opts);
+}