AngularJS watch array of objects for data change
$watch only evaluate string or function parameter in its first argument. Change your $watch like this :
$scope.$watch('cart.name + cart.id + cart.amount', $scope.updateCart());OR
$scope.$watch('cart', $scope.updateCart, true);See reference API
It is a common mistake to use a variable as the first parameter to the watch expression.
For $scope.cart, you should use the string cart:
$scope.$watch('cart', function () {...}, true)AngularJs has a new watch method, $watchCollection. It is basically the same as $watch with the object equality option set to true, to watch for a change in a property or an array item.
$scope.$watchCollection('cart', function () {...});Documentation: $watchCollection.