Delaying activation of watchers to the next tick guarantees consistent behavior between all implementations.
Additionally it eliminates the following problem:
Two defer()'s are set up with the first one immediately disabled
Second defer()'s callback is called and enables the first defer()'s watcher
Executes defer() in same tick or next tick?
If the answer is same tick, what happens in the following scenario:
An immediately disabled defer() and a delay($msDelay = 0) are set up
The delay()'s callback enables the defer()'s watcher
Executes defer() callback in same tick or next tick?
Doing it in same tick violates the requirement that defers are called before any other watchers in the same tick.
We get similar problems with e.g. delay() and repeat() (if their timer all expired now, but we require order to be preserved).
Thus we need to pretty much delay the activation of enable() to the next tick to avoid potential ambiguity or different behaviors depending on when exactly the enable() or watcher registration happened.
Delaying activation of watchers to the next tick guarantees consistent behavior between all implementations.
Additionally it eliminates the following problem:
If the answer is same tick, what happens in the following scenario:
We get similar problems with e.g. delay() and repeat() (if their timer all expired now, but we require order to be preserved).
Thus we need to pretty much delay the activation of enable() to the next tick to avoid potential ambiguity or different behaviors depending on when exactly the enable() or watcher registration happened.