How to declare directive or service i can use like a function in AngularJS expression

Question

I have many functions to convert Datetime format. I'd like to create a directive or a service to call these functions everywhere in my project.

Here is one of my functions.

$scope.formatDateTime = function (item) {
    if (item != null) {

        var d = moment().utc();
        if (item instanceof Date)
            d = new moment(item).utc();

        else if (item instanceof moment)
            d = item;

        else
            d = new moment(item, "YYYY-MM-DD HH:mm Z").utc();

        if (d != null) {

            moment.locale($rootScope.language);
            var strReturn = d.format("L LT");
            return strReturn;
        }
    }

    return null;
};

My problem is i have to copy my functions in every controller where i need to use them, so i'd like to call a service or directive, i don't really know what exactly, to call these functions like below :

<div>{{formatDateTime(dateToConvert)}}</div>

Answer 1

best solution is to create a custom filter

.filter('dateFilter', function() {
    return function(item) {
        if (item != null) {
            var d = moment().utc();
            if (item instanceof Date)
                d = new moment(item).utc();
            else if (item instanceof moment)
                d = item;
            else
                d = new moment(item, "YYYY-MM-DD HH:mm Z").utc();
            if (d != null) {
                moment.locale($rootScope.language);
                var strReturn = d.format("L LT");
                return strReturn;
            }
        }
        return null;
    }
})

in the html, call like this

<div>{{dateToConvert | dateFilter}}</div>