Publish order

[petronellius]

I have parent component and its child component, both subscribed on same event through EA. When event is published, callback in child component is called before parent callback. I would expect that callbacks are fired in same order as they were registered. Wouldn't be better if EA uses FIFO instead of LIFO?

[StrahilKazlachev]

So, long time ago I stumbled upon this too. The answer I got was:

• the EventAggregator does not guarantee any order of invocation
• the current behavior is because of perf

Changing this now will be a breaking change.
Could be possible to add an option to control to iteration direction, but that will be applicable only to explicitly created instances. Changing the global one will be a breaking change, which could even break the framework itself.

[petronellius]

I understand that it will be a breaking change but still thinking about it as expected behaviour. Option to control iteration direction would be solution. It could be application wide option and every instance of EA in app will accept it.

[StrahilKazlachev]

For reference:
#27 (comment)
#27 (comment)

[fkleuver]

Publish loop speed aside, invocation order could also be changed by using unshift instead of push here: https://github.com/aurelia/event-aggregator/blob/master/src/index.js#L110

Toggling that behavior with a flag could be done with a constructor argument to the EA as well as with a third argument to the subscribe method, defaulting to LIFO to ensure it isn't a breaking change.

Shouldn't be a big deal to add this option.