#4 Allow passing a function to the url parameter

Author: pladaria

README.md

@@ -17,8 +17,9 @@ WebSocket that will automatically reconnect if the connection is closed.
 - Handle connection timeouts
 - Full test coverage
 - Debug mode
-- Fast close (new in version 3)
+- Fast close
 - AMD build available (see dist folder)
+- Allows changing server URL
 
 ## Install
 
@@ -61,6 +62,21 @@ rws.addEventListener('open', () => {
 });
 ```
 
+### Update URL
+
+The `url` parameter also accepts a `function` so you have a chance to update the URL before connecting:
+```
+const ReconnectingWebSocket = require('reconnecting-websocket');
+
+const urls = ['ws://my.site.com', 'ws://your.site.com', 'ws://their.site.com'];
+let urlIndex = 0;
+
+// Round robin url provider
+const getUrl = () => urls[urlIndex++ % urls.length];
+
+const rws = new ReconnectingWebSocket(getUrl);
+```
+
 ### Configure
 
 #### Default options

dist/index.d.ts

@@ -1,4 +1,4 @@
-declare const ReconnectingWebsocket: (url: string, protocols?: string | string[], options?: {
+declare const ReconnectingWebsocket: (url: string | (() => string), protocols?: string | string[], options?: {
     constructor?: new (url: string, protocols?: string | string[]) => WebSocket;
     maxReconnectionDelay?: number;
     minReconnectionDelay?: number;

dist/index.js

@@ -114,7 +114,8 @@ var ReconnectingWebsocket = function (url, protocols, options) {
         }
         log('connect');
         var oldWs = ws;
-        ws = new config.constructor(url, protocols);
+        var wsUrl = (typeof url === 'function') ? url() : url;
+        ws = new config.constructor(wsUrl, protocols);
         connectingTimeout = setTimeout(function () {
             log('timeout');
             ws.close();

index.ts

@@ -63,7 +63,7 @@ const reassignEventListeners = (ws: WebSocket, oldWs: WebSocket, listeners) => {
 };
 
 const ReconnectingWebsocket = function(
-    url: string,
+    url: string | (() => string),
     protocols?: string|string[],
     options = <Options>{}
 ) {
@@ -134,7 +134,8 @@ const ReconnectingWebsocket = function(
 
         log('connect');
         const oldWs = ws;
-        ws = new (<any>config.constructor)(url, protocols);
+        const wsUrl = (typeof url === 'function') ? url() : url;
+        ws = new (<any>config.constructor)(wsUrl, protocols);
 
         connectingTimeout = setTimeout(() => {
             log('timeout');

test/test.js

@@ -32,6 +32,21 @@ test.cb('global WebSocket is used if available', t => {
     };
 });
 
+test.cb('url provider', t => {
+    t.plan(1);
+    const wss = new WSS({port: PORT});
+
+    const getUrl = () => url;
+    const ws = new RWS(getUrl, null, {maxRetries: 0, constructor: HWS});
+
+    ws.onopen = () => {
+        t.pass('Connected');
+        ws.close(1000, '', {keepClosed: true});
+        wss.close();
+        t.end();
+    }
+});
+
 test('connection status constants', t => {
     const ws = new RWS(url, null, {constructor: HWS});
     t.is(ws.CONNECTING, 0);