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Now that the performance difference between $broadcast and $emit has been eliminated, is there any reason to prefer $scope.$emit to $rootScope.$broadcast?
They are different, yes.
$emit is restricted to the scope hierarchy (upwards) - this may be good, if it fits your design, but it seems to me a rather arbitrary restriction.
$rootScope.$broadcast works across all that choose to listen to the event, which is a more sensible restriction in my mind.
Am I missing something?
EDIT:
To clarify in response to an answer, the direction of the dispatch is not the issue I'm after. $scope.$emit dispatches the event upwards, and $scope.$broadcast - downwards. But why not always use $rootScope.$broadcast to reach all the intended listeners?
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We can say that $rootscope is available to all the controllers whereas $scope is available only to the controller that created it.
The $rootScope. $broadcast is used to broadcast a “global” event that can be caught by any listener of that particular scope. The descendant scopes can catch and handle this event by using $scope.
Both $broadcast() and $emit() allow you to raise an event in your AngularJS application, using the event system of $scope and $rootScope . Again, there is no equivalent to this in modern Angular. If you are looking for a permanent fix during your migration to Angular, you will need an architectural level solution.
The difference between $broadcast() and $emit() is that the former sends the event from the current controller to all of its child controllers. That means $broadcast() sends an even downwards from parent to child controllers. The $emit() method, on the other hand, does exactly opposite.
tl;dr (this tl;dr is from @sp00m's answer below)
$emitdispatches an event upwards ...$broadcastdispatches an event downwards
Detailed explanation
$rootScope.$emit only lets other $rootScope listeners catch it. This is good when you don't want every $scope to get it. Mostly a high level communication. Think of it as adults talking to each other in a room so the kids can't hear them.
$rootScope.$broadcast is a method that lets pretty much everything hear it. This would be the equivalent of parents yelling that dinner is ready so everyone in the house hears it.
$scope.$emit is when you want that $scope and all its parents and $rootScope to hear the event. This is a child whining to their parents at home (but not at a grocery store where other kids can hear).
$scope.$broadcast is for the $scope itself and its children. This is a child whispering to its stuffed animals so their parents can't hear.
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