What is parentValueWatch in AngularJS?

Question

I use batarang to determine the source of some performance issues. One of the biggest culprits was my own code, but this parent thing ValueWatch now heads the diagrams, and I have no idea where it is or what launches it. My brains are lying on the floor from so much googling ... does anyone know?

(AngularJS v1.2.24)

Answer 1

ParentValueWatch is when a directive checks in its parent area the visibility of a change in some values ​​and, therefore, must be changed itself.

Consider a simple directive

 { restrict:"AE", scope:{ foo:'=' } } 

Now let's say in the parent scope, foo is an object.

 $parent.$scope.foo = { bar:"zim" } 

Each cycle of $digest , for the child $ region, it is necessary to check the value of the parent region foo and each of its properties.

If foo was really a big and deeply nested object, it would take a lot of time, so it takes so long.

Inside HTML, it might look like this:

 <div parent-directive> <div foo-directive foo=bar></div></div> 

One quick task is to “dry” the values ​​using ng-init.

 <div parent-directive> <div foo-directive ng-init='zug={bar:$parent.foo.bar}' foo=zug></div></div> 

Now the value tied to the new object. You lose easy binding, but gain performance.

It is always a compromise.