getTimezoneOffsetHoursAndMinutes -- Really, is this not already somewhere?

getTimezoneOffsetHoursAndMinutes.js

    // name is still bad, have yet to figure what would be more correct
    // sign change differences make re-using the TimezoneOffset verbage
    // confusing
    Date.prototype.getTimezoneOffsetHoursAndMinutes = function(){
      // offset in minutes
      var tzo = this.getTimezoneOffset();
      // determine 'direction' from GMT we are
      // if offset is positive, we're 'in the past'
      var behindGMT = tzo > 0;
      // work in positive
      tzo = Math.abs(tzo);
      // find our hour and minute 'parts'
      var hours = Math.floor(tzo/60);
      var minutes = tzo % 60;
      // pad, really only ever have 1 0 padding max
      // 2 digits
      minutes = ("0"+minutes+"").slice(-2);
      hours = ("0"+hours+"").slice(-2);
      // add our indication as to what side of GMT
      // we're on
      if (behindGMT){ hours = "-" + hours; }
      //done
      return hours + ":" + minutes;
    };