Best List page validation example

var answer = confirm ("Are you having fun?")
if (answer)
alert ("Woo Hoo! So am I.")
else
alert ("Darn. Well, keep trying then.")



// Validate the PTO Request input
function validateInput() {
    startDate = getValueWithFieldName('input', 'Request Start Date', 'ff1_new');
    endDate = getValueWithFieldName('input', 'Request End Date', 'ff2_new');
    //alert(startDate + endDate);
    startYear = startDate.substring(startDate.length, startDate.length - 4);
    endYear = endDate.substring(endDate.length, endDate.length - 4);
    //alert(startYear + endYear);
    if(startYear != endYear) {
        return 'Start date and end date must be in the same year.  To enter a PTO request which crosses into the next year, please enter two requests.';
    }
    if(startDate.length == 0) {
        return 'Please enter a start date.';
    }
    if(endDate.length == 0) {
        return 'Please enter an end date.';
    }
    return '';
}

// getValueWithFieldName: Get a form field value using its tagName, fieldname, and identifier to find it in the page
// Arguments:
//        tagName:    The type of input field (input, select, etc.)
//        fieldName:    The name of the list column
//        identifier:    The identifier for the instance of the fieldName (ff1, ff2, etc.)
//
    function getValueWithFieldName(tagName, fieldName, identifier) {
        //alert('getValueWithFieldName: tagName=' + tagName + ' fieldname=' + fieldName + ' identifier' + identifier);
        var theInput = getTagFromIdentifierAndFieldname(tagName, fieldName, identifier);
        //alert('getValueWithFieldName: theInput.id=' + theInput.id + ' theInput.value=' + theInput.value);
        return theInput.value;
    }

// getTagFromIdentifierAndFieldname: Get an input field's tag object using its tagName, fieldname, and identifier to find it in the page
// Arguments:
//        tagName:    The type of input field (input, select, etc.)
//        fieldName:    The name of the list column
//        identifier:    The identifier for the instance of the fieldName (ff1, ff2, etc.)
//
    function getTagFromIdentifierAndFieldname(tagName, fieldName, identifier) {
        //alert('getTagFromIdentifierAndTitle: tagName=' + tagName + ' fieldname=' + fieldName + ' identifier' + identifier);
        var len = identifier.length;
        var tags = document.getElementsByTagName(tagName);
        for (var i=0; i < tags.length; i++) {
            if (tags[i].title == fieldName) {
                //alert('HIT tags[' + i + '].title' + tags[i].title + ' tags[' + i + '].id=' + tags[i].id + ' identifier=' + identifier);
                if((tags[i].id == identifier) || (tags[i].id.indexOf(identifier) > 0)) {
                    return tags[i];
                }
            }
        }
        return null;
    }



<td nowrap="" class="ms-vb">
    <input type="button" value="Submit" name="btnSubmit">
     <xsl:attribute name="onclick">
      errmsg = validateInput();
      if(errmsg.length > 0) {
       alert(errmsg);
      } else {
       <xsl:value-of select="ddwrt:GenFireServerEvent('__commit;__redirectsource')" />
      }
     </xsl:attribute>
    </input>
    <input type="button" value="Cancel" name="btnCancel" onclick="javascript: {ddwrt:GenFireServerEvent('__cancel;__redirectsource')}" />
   </td>