validateDate

var DATE_REGEX  = /^(\d{2})-(\d{2})-(\d{4})$/

////////////////////////////////////////////////////////////////////////////////
//                                                                            //
// validateDate([object|string] oHTMLInputElement) - Validates a date value   //
// ===============================================                            // 
//   You can pass in the id to an <input> Element, an actual                  //
//   oHTMLInputElement or an actual date value in the form of a string        //
//                                                                            //
////////////////////////////////////////////////////////////////////////////////
function validateDate(oHTMLInputElementOrDateValue) {
  var theDateValueToValidate = "";
  var theValidatedDateValue = false;
  var bIsInputElement = false;
  if (typeof(oHTMLInputElementOrDateValue)=="string")  {
    var oHTMLInputElement = document.getElementById(oHTMLInputElementOrDateValue);
    if (oHTMLInputElement && typeof(oHTMLInputElement=="object") && (oHTMLInputElement.tagName=="INPUT")) {
      theDateValueToValidate = oHTMLInputElement.value;
      bIsInputElement = true;
    } else {
      // Presumably they just passed in a date string
      theDateValueToValidate = oHTMLInputElementOrDateValue;
      bIsInputElement = false;
    }
  } else {
    // They have passed in an Object
    if (typeof(oHTMLInputElementOrDateValue=="object") && (oHTMLInputElementOrDateValue.tagName=="INPUT")) {
      var oHTMLInputElement = oHTMLInputElementOrDateValue;
      theDateValueToValidate = oHTMLInputElement.value;
      bIsInputElement = true;
    }
  }
  // If we have a date value to actually validate, let's get started
  if (theDateValueToValidate != "") {
    var theDateValue = theDateValueToValidate.replace(/\//g,"-");  // Ruby-side only accepts hyphens
    if (DATE_REGEX.test(theDateValue)) {
      theValidatedDateValue = theDateValue;
    } else {
      if (theDateValue.indexOf('-') > -1) {
        var theMonth = theDateValue.split('-')[0];
        var theDay   = theDateValue.split('-')[1];
        var theYear  = theDateValue.split('-')[2];
        theMonth = parseInt(theMonth).PadWithZero();            // If they've entered a single digit for either Day or Month, pad with zero accordingly
        theDay   = parseInt(theDay).PadWithZero();
        if (theYear.length==2) { theYear = "20" + theYear; }    // If they've entered a two-digit year, assume it's in the 21st century
        theDateValue = theMonth + "-" + theDay + "-" + theYear; // Rebuild the date. Hopefully this will work
        if (DATE_REGEX.test(theDateValue)) {
          theValidatedDateValue = theDateValue;
        }
      }
      // If we get to this point and none of our efforts have worked to format the date as "required", throw an error (if they are using an INPUT element)
      if (!theValidatedDateValue && bIsInputElement) {
        alert("ERROR: Date must be formatted as follows:\n\n\tDD-MM-YYYY\n\nPlease correct before continuing");
        oHTMLInputElement.focus();
      }
    }
  }
  if (bIsInputElement && theValidatedDateValue) {
    oHTMLInputElement.value = theValidatedDateValue;
  }
  return theValidatedDateValue;
}

Here is a somewhat badass Date Validator routine I wrote today that takes in either a string date value or an Element Object and validates the date to be formatted as DD-MM-YYYY.

I wrote it for use by a Ruby on Rails application, but it's pretty handy as a general library function.

Shannon Norrell