Following is a sample of my object array.

```
$scope.arr = [{"A":"a","B":"b"},{"A":"c","B":"d"},{"A":"e","B":"f"},{"A":"g","B":"h"}];

```

Now I want trigger a function whenever property "A" value changes. Basically to get the count of "A" with a **not empty** value. Following are the sample scenarios need to trigger.

* If value of "A" changed for a newly added object to the array.
* If object removed where property "A" contains a value.
* If value added to empty "A" in a object
* If existing value emptied of "A" in a object

I have gone through Angular watch documentation and it is a possible solution. But my problem is how to watch for the **specific property("A")** in **any object** of array.

Appreciate any help for this. 

If no possible solution in Angular, is there any alternative solution with underscore.js ?