Phone Number Formatter TypeScript

FormatTel.ts

/// <reference path="../tsd/angularjs/angular.d.ts"/>

module AppName {
    class TelFilter {
        constructor(tel) {
            if (!tel) { return ''; }

            var value = tel.toString().trim().replace(/^\+/, '');

            if (value.match(/[^0-9]/)) {
                return tel;
            }

            var country, city, number;

            switch (value.length) {
                case 10: // +1PPP####### -> C (PPP) ###-####
                    country = 1;
                    city = value.slice(0, 3);
                    number = value.slice(3);
                    break;

                case 11: // +CPPP####### -> CCC (PP) ###-####
                    country = value[0];
                    city = value.slice(1, 4);
                    number = value.slice(4);
                    break;

                case 12: // +CCCPP####### -> CCC (PP) ###-####
                    country = value.slice(0, 3);
                    city = value.slice(3, 5);
                    number = value.slice(5);
                    break;

                default:
                    return tel;
            }

            if (country === 1) {
                country = '';
            }

            number = number.slice(0, 3) + '-' + number.slice(3);

            return (country + ' (' + city + ') ' + number).trim();
        };
    }

    angular.module('AppName').filter('tel', function(){
        return TelFilter;
    });
}