binding the same handler to the same event with once() can have unexpected results

I haven’t investigated to precisely determine the mechanism of the bug, but the behavior i saw was that binding the same handler to the same event with once multiple times would remove the wrong handler after firing.

so for example, you have an object which provides a token: myObject.getToken(), but my object is instantiated by an asynchronous process, you might write code like:

let tokenPromise = ()=>{
  if(myObject) {
    return new Promise((resolve) => {
        resolve(myObject.getToken())
    })
  }
  return new Promise((resolve)=>{
      emitter.once('MY_OBJECT_CREATED', ()=>{
        resolve(myObject.getToken())
      })
  })
}

multiple calls to tokenPromise results in the wrong handlers being unbound by once, i believe to confusion around the value of ‘fn’ within the once() method.

this seems to resolve the issue:

    once: function once (name, handler) {
      function fn (a, b, c) {
        app.off(name, this);
        handler(a, b, c);
      }

      return app.on(name, fn.bind(fn))
    }

[nihlton]

also, just my two cents, but this isn’t ideal:

fn.sourceString = handler.toString();

what if i’m using ‘sourceString’? or what if i’m not expecting any additional properties on the handler? just my opinion, but you shouldn’t modify the handlers passed to you…

but its your show 😃

thanks for looking into the issue.

[tunnckoCore]

Heya! Thanks for the report. I think problems mainly come from .off. Can you try the same example with .on method and report back, I believe it will have the same problem.

this seems to resolve the issue:

Mainly, I don’t want to rely on this, bind, apply and etc. The only thing where i found a need for .apply is in the .emit, because is the smallest solution to not call handlers with undefined - example:

emitter.on('foo', function (a, b, c) {
  console.log(a, b, c) // => 1, undefined, undefined
  console.log(arguments.length) // => 3, it should be 1
})
emitter.emit('foo', 1)