Best Practices

The use of anonymous or local functions

Use anonymous or local functions only, if you don't intend to unsibscribe them again as the function reference is lost after leaving the function. The following examples illustrate the problem:

eventBus.subscribe('testEvent', () => {
  console.log('testEvent');
});

eventBus.unsubscribe('testEvent', () => {
  console.log('testEvent');
});

eventBus.raise('testEvent'); // prints 'testEvent'

const sub = () => {
  const func = () => {
    console.log('testEvent');
  };
  eventBus.subscribe('testEvent', func);
}

const unsub = () => {
  const func = () => {
    console.log('testEvent');
  };
  eventBus.unsubscribe('testEvent', func);
}

sub();
unsub();
eventBus.raise('testEvent'); // prints 'testEvent'

To fix this, keep the function reference outside the local scope:

const func = () => {
  console.log('testEvent');
};

const sub = () => {
  eventBus.subscribe('testEvent', func);
}

const unsub = () => {
  eventBus.unsubscribe('testEvent', func);
}

sub();
unsub();
eventBus.raise('testEvent'); // prints nothing

One Shot Handlers

You can use local functions as one shot handlers like this:

const func = () => {
  console.log('testEvent');
  eventBus.unsubscribe('testEvent', func);
};
eventBus.subscribe('testEvent', func);
eventBus.raise('testEvent'); // prints 'testEvent'
eventBus.raise('testEvent'); // prints nothing