javascript handle local and UTC time and string conversion

datetime_functions.js

    function convert_to_utc (today){ 
	var localoffset = -(today.getTimezoneOffset()/60);
	//var destoffset = -4; 
	
	//var offset = destoffset-localoffset;
	var offset = localoffset;
	var d = new Date( today.getTime() + offset * 3600 * 1000);
	return d;
    }
    
    function date_to_string(date){

	var dd = date.getDate();
	var mm = date.getMonth()+1; //January is 0!
	
	var yyyy = date.getFullYear();
	if(dd<10){
	    dd='0'+dd;
	} 
	if(mm<10){
	    mm='0'+mm;
	} 
	var ret = yyyy+'-'+mm+'-'+dd;
	return ret;
    }
    
    function padZero(number){
	return number <= 9 ? ("0"+number).slice(-2) : number;
    }
    
    function localTimeStringToUTCTimeString (localTimeString){
      var date = new Date(localTimeString);
      if (isNaN(date)) {
	throw new Error("date parsing error: " + localTimeString);
      }
      return (date.getUTCFullYear()+"-"+ padZero(date.getUTCMonth()+1)+"-"+padZero(date.getUTCDate())+" "
	      +padZero(date.getUTCHours())+":"+padZero(date.getUTCMinutes())+":"+padZero(date.getUTCSeconds()));
    }

    function localTimeToUTCTimeString (date){
      //var date = new Date(localTimeString);
      if (isNaN(date)) {
	throw new Error("date parsing error: " + localTimeString);
      }
      return (date.getUTCFullYear()+"-"+ padZero(date.getUTCMonth()+1)+"-"+padZero(date.getUTCDate())+" "
	      +padZero(date.getUTCHours())+":"+padZero(date.getUTCMinutes())+":"+padZero(date.getUTCSeconds()));
    }    

    function stdTimezoneOffset(date)  {
	var jan = new Date(date.getFullYear(), 0, 1);
	var jul = new Date(date.getFullYear(), 6, 1);
	return Math.max(jan.getTimezoneOffset(), jul.getTimezoneOffset());
    }
    
    //@purpose: given t as UTC timestring, return an object for its localTimeString and timeZoneString
    //@param   t : String,
    //@return: { timeString: time, timeZone: timeZoneString }
    function localizeTime (t)
    {
      //var d=new Date(t.replace("T", " ")+" UTC");
      var d=new Date(t+"Z");
      var currentTimeZoneOffsetInHours = d.getTimezoneOffset() / 60;
      var sign;
      if (currentTimeZoneOffsetInHours > 0){
	sign = "-";
      }else{
	sign = "+";
      }
      var timeZone = "GMT "+sign+currentTimeZoneOffsetInHours;
      var isDst = d.getTimezoneOffset() < stdTimezoneOffset(d);
      if (timeZone == "GMT -6" && isDst){
	timeZone = "MDT";
      }else if (timeZone == "GMT -7" && !isDst){
	timeZone = "MST";
      }else if(timeZone == "GMT -7" && isDst){
	timeZone = "PDT";
      }else if(timeZone == "GMT -8" && !isDst){
	timeZone = "PST";
      }else if(timeZone == "GMT -4" && isDst){
	timeZone = "EDT";
      }else if(timeZone == "GMT -5" && !isDst){
	timeZone = "EST";
      }
      var timeString = d.getFullYear()+"-"+(d.getMonth() + 1) + "-" + d.getDate() +" " +
		  d.getHours() + ":" + d.getMinutes() + ":" + d.getSeconds();
      return { timeString: timeString, timeZone: timeZone };
      //return (d.toString());
    }