Fix: Handle race condition when WebSocket is already open

[Al-ex-ei]

Problem

When webSocketFactory returns an already open WebSocket, the onopen callback never triggers and CONNECT frame is not sent.

Solution

Added readyState check: if already open, call the handler immediately; otherwise set onopen.

[Al-ex-ei]

@kum-deepak take a look please

[kum-deepak]

Many thanks for the PR. I understand how it works. I also know why it is needed.

I will merge it after writing test cases to cover it.

I am curious, how did you encounter this race condition? I will add those to the documentation or FAQs.

[Al-ex-ei]

It's a bit unusual case.

I was optimizing the time to Interactive metric for my app. Receiving data via stomp was the longest part of loading for a significant number of users.

So I decided to load the stompjs library and create the WebSocket connection in parallel. When stompjs is ready, I create a client and provide it with the WebSocket, but the WebSocket state could be different in different cases (different connection speeds, network conditions, locations, etc.)

In some cases, the WebSocket is already in the OPEN

[kum-deepak]

I have added a test case, see

stompjs/spec/unit/connection.spec.js

Line 47 in 998a6de

it('Connect with a websocket that is already open', function (done) {

[kum-deepak]

Merged and published as v7.3.0-beta.2.