add method for new /aliases endpoint

src/base-apis.js

@@ -1119,6 +1119,21 @@ MatrixBaseApis.prototype.deleteAlias = function(alias, callback) {
     );
 };
 
+/**
+ * @param {string} roomId
+ * @param {module:client.callback} callback Optional.
+ * @return {Promise} Resolves: an object with an `aliases` property, containing an array of local aliases
+ * @return {module:http-api.MatrixError} Rejects: with an error response.
+ */
+MatrixBaseApis.prototype.unstableGetLocalAliases =
+function(roomId, callback) {
+    const path = utils.encodeUri("/rooms/$roomId/aliases",
+        {$roomId: roomId});
+    const prefix = PREFIX_UNSTABLE + "/org.matrix.msc2432";
+    return this._http.authedRequest(callback, "GET", path,
+        null, null, { prefix });
+};
+
 /**
  * Get room info for the given alias.
  * @param {string} alias The room alias to resolve.

src/client.js

@@ -4797,6 +4797,19 @@ MatrixClient.prototype.doesServerSupportSeparateAddAndBind = async function() {
         || (unstableFeatures && unstableFeatures["m.separate_add_and_bind"]);
 };
 
+/**
+ * Query the server to see if it lists support for an unstable feature
+ * in the /versions response
+ * @param {string} feature the feature name
+ * @return {Promise<boolean>} true if the feature is supported
+ */
+MatrixClient.prototype.doesServerSupportUnstableFeature = async function(feature) {
+    const response = await this.getVersions();
+    if (!response) return false;
+    const unstableFeatures = response["unstable_features"];
+    return unstableFeatures && !!unstableFeatures[feature];
+};
+
 /**
  * Get if lazy loading members is being used.
  * @return {boolean} Whether or not members are lazy loaded by this client