Require and re-use $watch feature for AngularJS expressions, which has a syntax similar to a directive's require: '^expression'. Walks up the scope hierarchy until a $watch on an identical expression is found (that was created with ngWatchRequire syntax) and re-uses it.

bower install angular-watch-require

Add 'ngWatchRequire' to your application or module.

The expression syntax is baked into $parse and can be used in $scope.$watch[*], templates, and directives.

Use it in controllers

$scope.$watch('?^myModel', function(){})

Use it in templates

<span>{{?^myModel}}</span>
<span ng-bind="?^myModel"></span>

Options

• '?expression' - Attempt to attach to already defined $watch on current $scope, creating a new $watch if necessary.
• '^expression' - Attach to an already defined $watch on current $scope or first parent.
• '?^expression' - Attempt to attach to already defined $watch on current $scope or first parent. Creating a new $watch on current $scope necessary.

AngularJS 1.3 introduces a $$watchDelegate property on expressions returned by the $parse service. Decorating the $parse service allows us to wrap the expression with a delegate that performs our custom logic.

Use with care. A proper understanding of scopes' prototypical inheritance and the mechanics of $scope.$digest() are recommended.

angular-watch-when - Makes use of this module to produce 'one-time' watches that recycle when another expression changes.