Watch ngModel value change from directive on parent element

Question

I have a directive which watches for change in an input field

directive('autocomplete', function(){
    return {
        link: function(scope, element, attrs){
            scope.$watch(attrs.ngModel, function(){
                console.log('change');
            });
        }
    };
});

This works fine on the following element

<input type='text' ng-model='searchTerm' autocomplete>

But what if I was to put my directive on an ancestor element, like this:

<div autocomplete>
    <input type='text' ng-model='searchTerm'>
</div>

How could I still watch the input for change then?

hon2a · Accepted Answer · 2014-12-14 16:47:01Z

Simply put: you could, but you shouldn't.

First, the ngModel directive has a controller. Its $viewChangeListeners property is probably what you'd really want to use (as your "autocomplete" directive is probably going to be looking out just for view value changes). You can just push your change listener into that array.

Second (and more to the point), you shouldn't direct that kind of functionality from the ancestor element only. If you wish to interact with ngModel, you'd better put your directive right on the element using it or its descendant (not an option with an <input>). This doesn't stop you from putting some common logic on an ancestor and interacting with that ancestor (much like ngModel interacts with ngForm).

If you don't care about shoulds and shouldn'ts, you can always either

put a name on your input and get the ngModelController from the ngForm (if your directive is under it), or
find the <input> and get the ngModelController using angular.element(...).controller('ngModel').

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