Simple factory provider for angular >1.4 that returns GMT string for local timezone.

gmtFactory.js

/**
 * Created by Oleg Galaburda on 26.09.15.
 */
(function(){
  angular.module('timezone.gmt', []).factory('gmtFactory', function() {
    function getTimezoneOffset(date){
      date = date || new Date();
      return date.getTimezoneOffset();
    }
    function intToString(num, length) {
      length = length || 2;
      var value = String(num);
      while(value.length<length) {
        value = '0' + value;
      }
      return value;
    }
    function minutesToGMT(num) {
      var hours = (num / 60) >> 0;
      var minutes = num % 60;
      return intToString(hours) + intToString(minutes);
    }
    function convertOffsetToGMT(offset) {
      var value = 'GMT';
      if(offset < 0) {
        value += '+';
        offset = -offset;
      }else value += '-';

      return value + minutesToGMT(offset);
    }
    function getGMTString(date) {
      return convertOffsetToGMT(getTimezoneOffset(date));
    }
    getGMTString.toString = getGMTString;
    getGMTString.byOffset = convertOffsetToGMT;
    return getGMTString;
  });
})();