It's expecting data from the WebSocket 'open' handler, but the handler will never supply any data. I guess it's possible that he modified the websocket code and never committed his changes.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
I think you might have to ask Marcus who wrote it - maybe file an issue on the Github page?
Looks to me like it's failing here: https://github.com/AverageMarcus/pusher-websocket-espruino/blob/master/pusher.js#L89
It's expecting data from the WebSocket 'open' handler, but the handler will never supply any data. I guess it's possible that he modified the websocket code and never committed his changes.
However: you could try just deleting these 3 lines? https://github.com/AverageMarcus/pusher-websocket-espruino/blob/master/pusher.js#L88-90
Thst might fix it