How to wait for a WebSocket's readyState to change

Question

I'm trying to implement a WebSocket with a fallback to polling. If the WebSocket connection succeeds, readyState becomes 1, but if it fails, readyState is 3, and I should begin polling.

I tried something like this:

var socket = new WebSocket(url); socket.onmessage = onmsg; while (socket.readyState == 0) { } if (socket.readyState != 1) {     // fall back to polling     setInterval(poll, interval); } 

I was expecting socket.readyState to update asynchronously, and allow me to read it immediately. However, when I run this, my browser freezes (I left it open for about half a minute before giving up).

I thought perhaps there was an onreadyStateChanged event, but I didn't see one in the MDN reference.

How should I be implementing this? Apparently an empty loop won't work, and there is no event for this.

Answer 1

This is simple and it work perfectly... you can add condition about maximal time, or number of try to make it more robust...

function sendMessage(msg){     // Wait until the state of the socket is not ready and send the message when it is...     waitForSocketConnection(ws, function(){         console.log("message sent!!!");         ws.send(msg);     }); }  // Make the function wait until the connection is made... function waitForSocketConnection(socket, callback){     setTimeout(         function () {             if (socket.readyState === 1) {                 console.log("Connection is made")                 if (callback != null){                     callback();                 }             } else {                 console.log("wait for connection...")                 waitForSocketConnection(socket, callback);             }          }, 5); // wait 5 milisecond for the connection... }