Arguments.length is greater than what it is

[etanxing]

self.$dispatch('application.progress.update', 'start', 80);

When handle this event:

this.$on('application.progress.update', function () {
   //It's true, arguments: 'start', 80 and undefined
   arguments.length === 3
})

Is it an expected behavior?

[marfalkov]

More: http://jsfiddle.net/marfalkov/6L4cc/

The reason for this is happening on Line 66 of emitter.js (see here)

callbacks[i].call(this._ctx, a, b, c)

Not sure why 3 args are explicity being passed so I need to do more digging in the src.

[yyx990803]

Yeah this was a trick that greatly improved internal emitter performance because fn.call with fixed amount of args is much faster than fn.apply. But I guess in this case it causes confusion for the user. I will make the external version use apply instead.

[yyx990803]

fixed in 81ae36c