Refactor widget postMessage API.

src/WidgetMessagingEndpoint.js

@@ -0,0 +1,37 @@
+/*
+Copyright 2018 New Vector 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.
+*/
+
+
+/**
+ * Represents mapping of widget instance to URLs for trusted postMessage communication.
+ */
+export default class WidgetMessageEndpoint {
+    /**
+     * Mapping of widget instance to URL for trusted postMessage communication.
+     * @param  {string} widgetId    Unique widget identifier
+     * @param  {string} endpointUrl Widget wurl origin.
+     */
+    constructor(widgetId, endpointUrl) {
+        if (!widgetId) {
+            throw new Error("No widgetId specified in widgetMessageEndpoint constructor");
+        }
+        if (!endpointUrl) {
+            throw new Error("No endpoint specified in widgetMessageEndpoint constructor");
+        }
+        this.widgetId = widgetId;
+        this.endpointUrl = endpointUrl;
+    }
+}