This validates and returns various different time values in javascript

justin_time.js

//Author: Justin Obney
//This should return an array with validity and other info
// pass = [true, date object, regex match array, date object toString (for testing) ]
// fail = [false, "error message"]

// should return valid date objects the following:
// 8:00am     -standard w/ no preceding "0"
// 09:00am    -standard w/ preceding "0"
// 7:13p      -matches p to "PM"
// 14:35      -accepts 24 hour time
// 5a         -accepts hour + a for 5:00 AM
// 10am       -same with "am"
// 12 p        -same with " p"
// 5 pm        -same with " pm"

function checkTime(input, optional_date)  // if optional_date is omitted, returned date will use current date
  {
    var errorMsg = "",
        hour,
        min,
        timeofday;

    // regular expression to match required time format
    re = /^(\d{1,2})(:\d{2})?(\s?[ap]m?)?$/;

    if(input != '') {
      if(regs = input.match(re)) {
        if(parseFloat(regs[1]) > 0 && parseFloat(regs[1]) < 13) {
          // 12-hour time format
            if(regs[3]){
                //has am/pm
                hour = parseFloat(regs[1]);
                if (regs[3].toUpperCase().indexOf('P') != -1){
                    //its pm --> add 12
                    hour += 12;
                }
            } else {
                //no am/pm
                //assume am ???? throw error ????
                errorMsg = "Invalid value for AM/PM:";                
            }
        } else if(regs[1] < 24) {
            // 24-hour time format
            // assume pm
            hour = parseInt(regs[1]);
        } else {
            errorMsg = "Invalid value for hours: " + regs[1];
        }
          
        if(!errorMsg && regs[2]) {
            // has minutes field
            min = parseInt(regs[2].replace(':',''));
        } else {
            // has no minutes field.. assume :00
            min = 0;
        }
      } else {
        errorMsg = "Invalid time format: " + input;
      }
    }

    if(errorMsg != "") {
      return [false, errorMsg];
    }
    var today = (optional_date || new Date()) ,
        year = today.getYear(),
        month = today.getMonth(),
        day = today.getDate();
      
    var d = new Date(year + 1900, month, day, hour, min, 0, 0);
    
    function getStandardTime(time) {
        var hour, minute, tod = 'AM';
        if (time.getHours() > 12) {
            hour = time.getHours() - 12;
            tod = 'PM';
        } else {
            hour = time.getHours();
        }
        minute = time.getMinutes();
    
        var padHour = (hour < 10) ? '0' + hour : hour;
        var padMinute = (minute < 10) ? '0' + minute : minute;
    
        return padHour + ':' + padMinute + ' ' + tod;
    }
      
    return [ true, d, regs, d.toString(), getStandardTime(d) ];
 }