The main point of this post is that I want to avoid using $scope.$watch as it is taught to cause a performance decrease.
So imagine having one shared view partial/template, call it "mypage" with two different directives, call them "directive1" and "directive2", in it that share a data model, lets call it "awesomeData"
Maybe it looks something like this:
<div class="mypage-root">
<directive1 shared-data="awesomeData"></directive1>
<directive2 shared-data="awesomeData"></directive2>
</div>
Now obviously when "awesomeData" changes in either directive or the root view, the data changes in the other parts too (assuming it is two-way bound).
But what if i want something else to happen in directive2 when directive1 has updated the data model, like calling a function in directive2?
I could use a watcher but as mentioned, that is a performance decrease.
What other approaches are there and what is the "true" angular way to do this?