websocket hook

websocket-hook.js

//
// https://stackoverflow.com/questions/70205816/intercept-websocket-messages
//
function listen(fn){
  fn = fn || console.log;

  let property = Object.getOwnPropertyDescriptor(MessageEvent.prototype, "data");
  
  const data = property.get;

  // wrapper that replaces getter
  function lookAtMessage() {

    let socket = this.currentTarget instanceof WebSocket;

    if (!socket) {
      return data.call(this);
    }

    let msg = data.call(this);

    Object.defineProperty(this, "data", { value: msg } ); //anti-loop
    fn({ data: msg, socket:this.currentTarget, event:this });
    return msg;
  }
  
  property.get = lookAtMessage;
  
  Object.defineProperty(MessageEvent.prototype, "data", property);
}

listen( ({data}) => console.log(data))