flying-squid/src/lib/behavior.js

module.exports = (obj) => {
  return async (eventName, data, func, cancelFunc) => {
    let hiddenCancelled = false;
    let cancelled = false;
    let cancelCount = 0;
    let defaultCancel = true;
    const cancel = (dC=true, hidden=false) => { // Hidden shouldn't be used often but it's not hard to implement so meh
      if (hidden) hiddenCancelled = true;
      else {
        cancelled = true;
        cancelCount++;
      }
      defaultCancel = dC;
    };
    
    let resp;

    await obj.emitThen(eventName + '_cancel', data, cancel).catch((err)=> setTimeout(() => {throw err;},0));
    await obj.emitThen(eventName, data, cancelled, cancelCount).catch((err)=> setTimeout(() => {throw err;},0));

    if (!hiddenCancelled && !cancelled) {
      resp = func(data);
      if (resp instanceof Promise) resp = await resp.catch((err)=> setTimeout(() => {throw err;},0));
      if (typeof resp == 'undefined') resp = true;
    } else if (cancelFunc && defaultCancel) {
      resp = cancelFunc(data);
      if (resp instanceof Promise) resp = await resp.catch((err)=> setTimeout(() => {throw err;},0));
      if (typeof resp == 'undefined') resp = false;
    }
    await obj.emitThen(eventName + '_done', data, cancelled).catch((err)=> setTimeout(() => {throw err;},0));

    return resp;
  }
};