Check if newly created object exist in array (AngularJS specific) [duplicate]

The function toggleIntervention is called every time a check-box is checked/unchecked. It should push an object to array or remove it from the array depending if its checked/unchecked.

I am using indexOf to check if the object exist in the array, however the index is always -1 even if the object exists in the array. What am I missing?

    $scope.selectedInterventions=[];
    $scope.toggleIntervention = function(inputIntervention) {

        var intervention =  {
                cptCode:inputIntervention.service,
            description:inputIntervention.description,
                  notes:"intervention notes",
             targetDate:"11/11/2014",
         resolutionDate:"11/11/2014"
        };

        // The index always -1 even if the object exists in the array of selectedInterventions
        var idx = $scope.selectedInterventions.indexOf(intervention); 
        if (idx > -1) { 
            $scope.selectedInterventions.splice(idx, 1);
        } else {
            $scope.selectedInterventions.push(intervention);
        }
    };