update UI when hash changes

src/utils/ViewModel.js

@@ -0,0 +1,70 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+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.
+*/
+
+class EventEmitter {
+    constructor() {
+        this._handlersByName = {};
+    }
+
+    emit(name, ...values) {
+        const handlers = this._handlersByName[name];
+        if (handlers) {
+            for(const h of handlers) {
+                h(...values);
+            }
+        }
+    }
+
+    on(name, callback) {
+        let handlers = this._handlersByName[name];
+        if (!handlers) {
+            this._handlersByName[name] = handlers = new Set();
+        }
+        handlers.add(callback);
+        return () => {
+            this.off(name, callback);
+        }
+    }
+
+    off(name, callback) {
+        const handlers = this._handlersByName[name];
+        if (handlers) {
+            handlers.delete(callback);
+            if (handlers.length === 0) {
+                delete this._handlersByName[name];
+            }
+        }
+    }
+}
+
+export class ViewModel extends EventEmitter {
+    constructor(options) {
+        super();
+        this._options = options;
+    }
+
+    emitChange() {
+        this.emit("change");
+    }
+
+    get request() {
+        return this._options.request;
+    }
+
+    childOptions(options = {}) {
+        return Object.assign({request: this.request}, options);
+    }
+}