`task.once` is invalid in worker-executor.js

Describe the bug

task.once is invalid in client/src/templates/Challenges/utils/worker-executor.js.

To Reproduce

1. add a test in client/src/templates/Challenges/utils/worker-executor.test.js

   it('Task should emit handler once', () => {
     mockWorker();
     const testWorker = createWorker('test');
     const task = testWorker.execute('test');
     const handler = jest.fn();
     task.once('testOnce', handler);
   
     task.emit('testOnce', handler);
     task.emit('testOnce', handler);
     expect(handler).toBeCalledTimes(1);
   });
   

2. run this test

3. If task.once works well, then handler will be called just once.

4. However, handler is called twice time.

Expected behavior

handler should only be called once.

Analyze

There is only one parameter handler in the function self.removeListener on Line 141

https://github.com/freeCodeCamp/freeCodeCamp/blob/8f19b1926bc51c0149254fdd7a86ecb0708c6dd2/client/src/templates/Challenges/utils/worker-executor.js#L141

self.once = (event, listener) => {
  self.on(event, function handler(...args) {
    self.removeListener(handler);
    listener.apply(self, args);
  });
  return self;
};

But functionremoveListener needs two parameters (event and listener), since handler is type of function instead of type of string, so the program never enters the if judgment.

  self.removeListener = (event, listener) => {
    if (typeof self._events[event] !== 'undefined') {
      const index = self._events[event].indexOf(listener);
      if (index !== -1) {
        self._events[event].splice(index, 1);
      }
    }
    return self;
  };

Solution

Perhaps Line 141

https://github.com/freeCodeCamp/freeCodeCamp/blob/8f19b1926bc51c0149254fdd7a86ecb0708c6dd2/client/src/templates/Challenges/utils/worker-executor.js#L141

should be changed to

self.removeListener(event, handler);

and change Line 96

https://github.com/freeCodeCamp/freeCodeCamp/blob/8f19b1926bc51c0149254fdd7a86ecb0708c6dd2/client/src/templates/Challenges/utils/worker-executor.js#L96 to

task.done = new Promise((resolve, reject) => {
  task
    .on('done', data => resolve(data))
    .on('error', err => reject(err.message));
});

[ojeytonwilliams]

It’s a tricky one to migrate - I tried myself and it was a bit of a mess. However, with your changes the number of arguments should match up, so that should help the migration.

[ojeytonwilliams]

Awesome, I’m glad you were able to figure it out - that file is pretty confusing.