實施範例26

26.在表單中提供客戶端驗證並透過DOM加入錯誤文字訊息

這項技巧目的是使用客戶端腳本來驗證在表單上輸入的資料,如驗證失敗,錯誤訊息會以連結清單的方式顯示在所有欄位的上方,並把焦點移到錯誤訊息的位置上來吸引用戶注意,而且清單中的連結文字會帶領用戶連結到網頁內須重新輸入的欄位上。

範例:

這個例子會驗證一些必須填寫、和須要特定格式的欄位。
如發現錯誤,腳本會把錯誤信息清單加入DOM,並把焦點移到該訊息。

HTML 組件:
範例代碼:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>Form Validation</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<link href="css/validate.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="scripts/validate.js"/>
</head>
<body>

        <h1>Form Validation</h1>

        <p>The following form is validated before being submitted if scripting is available,
otherwise the form is validated on the server. All fields are required, except those
marked optional. If errors are found in the submission, the form is cancelled and
a list of errors is displayed at the top of the form.</p>

        <p> Please enter your details below. </p>

        <h2>Validating Form</h2>

        <form id="personalform" method="post" action="index.php">
<div class="validationerrors"/>
<fieldset>
<legend>Personal Details</legend>
<p>
<label for="forename">Please enter your forename</label>
<input type="text" size="20" name="forename" id="forename" class="string"
value=""/>
</p>
<p>
<label for="age">Please enter your age</label>
<input type="text" size="20" name="age" id="age" class="number" value=""/>
</p>
<p>
<label for="email">Please enter your email address</label>
<input type="text" size="20" name="email" id="email" class="email" value=""/>
</p>
</fieldset>
<p>
<input type="submit" name="signup" value="Sign up"/>
</p>
</form>
<h2>Second Form</h2>
<form id="secondform" method="post" action="index.php#focuspoint">
<div class="validationerrors"/>
<fieldset>
<legend>Second Form Details</legend>
<p>
<label for="suggestion">Enter a suggestion</label>
<input type="text" size="20" name="suggestion" id="suggestion"
class="string" value=""/>
</p>
<p>
<label for="optemail">Please enter your email address (optional)</label>
<input type="text" size="20" name="optemail" id="optemail"
class="optional email" value=""/>
</p>
<p>
<label for="rating">Please rate this suggestion</label>
<input type="text" size="20" name="rating" id="rating"
class="number" value=""/>
</p>
<p>
<label for="jibberish">Enter some jibberish (optional)</label>
<input type="text" size="20" name="jibberish" id="jibberish" value=""/>
</p>

            </fieldset>
<p>
<input type="submit" name="submit" value="Add Suggestion"/>
</p>
</form>
</body>
</html>

javascript 組件:用以驗證和顯示錯誤清單
範例代碼:

window.onload = initialise;

function initialise()
{
var objForms = document.getElementsByTagName('form');
var iCounter;

   // Attach an event handler for each form
for (iCounter=0; iCounter<objForms.length; iCounter++)
{
objForms[iCounter].onsubmit = function(){return validateForm(this);};
}
}

 

// Event handler for the form
function validateForm(objForm)
{
var arClass = [];
var iErrors = 0;
var objField = objForm.getElementsByTagName('input');
var objLabel = objForm.getElementsByTagName('label');
var objList = document.createElement('ol');
var objError, objExisting, objNew, objTitle, objParagraph, objAnchor, objPosition;
var strLinkID, iFieldCounter, iClassCounter, iCounter;

   // Get the id or name of the form, to make a unique
// fragment identifier
if (objForm.id)
{
strLinkID = objForm.id + 'ErrorID';
}
else
{
strLinkID = objForm.name + 'ErrorID';
}

   // Iterate through input form controls, looking for validation classes
for (iFieldCounter=0; iFieldCounter<objField.length; iFieldCounter++)
{
// Get the class for the field, and look for the appropriate class
arClass = objField[iFieldCounter].className.split(' ');
for (iClassCounter=0; iClassCounter<arClass.length; iClassCounter++)
{
switch (arClass[iClassCounter])
{
case 'string':
if (!isString(objField[iFieldCounter].value, arClass))
{
if (iErrors === 0)
{
logError(objField[iFieldCounter], objLabel, objList, strLinkID);
}
else
{
logError(objField[iFieldCounter], objLabel, objList, '');
}
iErrors++;
}
break;
case 'number':
if (!isNumber(objField[iFieldCounter].value, arClass))
{
if (iErrors === 0)
{
logError(objField[iFieldCounter], objLabel, objList, strLinkID);
}
else
{
logError(objField[iFieldCounter], objLabel, objList, '');
}
iErrors++;
}
break;

            case 'email' :
if (!isEmail(objField[iFieldCounter].value, arClass))
{
if (iErrors === 0)
{
logError(objField[iFieldCounter], objLabel, objList, strLinkID);
}
else
{
logError(objField[iFieldCounter], objLabel, objList, '');
}
iErrors++;
}
break;
}
}
}

   if (iErrors > 0)
{
// If not valid, display error messages
objError = objForm.getElementsByTagName('div');

// Look for existing errors
for (iCounter=0; iCounter<objError.length; iCounter++)
{
if (objError[iCounter].className == 'validationerrors')
{
objExisting = objError[iCounter];
}
}

      objNew = document.createElement('div');
objTitle = document.createElement('h2');
objParagraph = document.createElement('p');
objAnchor = document.createElement('a');

      if (iErrors == 1)
{
objAnchor.appendChild(document.createTextNode('1 Error in Submission'));
}
else
{
objAnchor.appendChild(document.createTextNode(iErrors + ' Errors in Submission'));
}
objAnchor.href = '#' + strLinkID;
objAnchor.className = 'submissionerror';

      objTitle.appendChild(objAnchor);
objParagraph.appendChild(document.createTextNode('Please review the following'));
objNew.className = 'validationerrors';

      objNew.appendChild(objTitle);
objNew.appendChild(objParagraph);
objNew.appendChild(objList);

// If there were existing error, replace them with the new lot,
// otherwise add the new errors to the start of the form
if (objExisting)
{
objExisting.parentNode.replaceChild(objNew, objExisting);
}
else
{
objPosition = objForm.firstChild;
objForm.insertBefore(objNew, objPosition);
}

      // Allow for latency
setTimeout(function() { objAnchor.focus(); }, 50);

// Don't submit the form
objForm.submitAllowed = false;
return false;
}

   // Submit the form
return true;
}

// Function to add a link in a list item that points to problematic field control
function addError(objList, strError, strID, strErrorID)
{
var objListItem = document.createElement('li');
var objAnchor = document.createElement('a');

// Fragment identifier to the form control
objAnchor.href='#' + strID;

   // Make this the target for the error heading
if (strErrorID.length > 0)
{
objAnchor.id = strErrorID;
}

   // Use the label prompt for the error message
objAnchor.appendChild(document.createTextNode(strError));
// Add keyboard and mouse events to set focus to the form control
objAnchor.onclick = function(event){return focusFormField(this, event);};
objAnchor.onkeypress = function(event){return focusFormField(this, event);};
objListItem.appendChild(objAnchor);
objList.appendChild(objListItem);
}

function focusFormField(objAnchor, objEvent)
{
var strFormField, objForm;

   // Allow keyboard navigation over links
if (objEvent && objEvent.type == 'keypress')
{
if (objEvent.keyCode != 13 && objEvent.keyCode != 32)
{
return true;
}
}

   // set focus to the form control
strFormField = objAnchor.href.match(/[^#]\w*$/);
objForm = getForm(strFormField);
objForm[strFormField].focus();
return false;
}

// Function to return the form element from a given form field name
function getForm(strField)
{
var objElement = document.getElementById(strField);

   // Find the appropriate form
do
{
objElement = objElement.parentNode;
} while (!objElement.tagName.match(/form/i) && objElement.parentNode);

   return objElement;
}

// Function to log the error in a list
function logError(objField, objLabel, objList, strErrorID)
{
var iCounter, strError;

   // Search the label for the error prompt
for (iCounter=0; iCounter<objLabel.length; iCounter++)
{
if (objLabel[iCounter].htmlFor == objField.id)
{
strError = objLabel[iCounter].firstChild.nodeValue;
}
}

   addError(objList, strError, objField.id, strErrorID);
}

// Validation routines - add as required

function isString(strValue, arClass)
{
var bValid = (typeof strValue == 'string' && strValue.replace(/^\s*|\s*$/g, '')
!== '' && isNaN(strValue));

   return checkOptional(bValid, strValue, arClass);
}

function isEmail(strValue, arClass)
{
var objRE = /^[\w-\.\']{1,}\@([\da-zA-Z\-]{1,}\.){1,}[\da-zA-Z\-]{2,}$/;
var bValid = objRE.test(strValue);

   return checkOptional(bValid, strValue, arClass);
}

function isNumber(strValue, arClass)
{
var bValid = (!isNaN(strValue) && strValue.replace(/^\s*|\s*$/g, '') !== '');

   return checkOptional(bValid, strValue, arClass);
}

function checkOptional(bValid, strValue, arClass)
{
var bOptional = false;
var iCounter;

   // Check if optional
for (iCounter=0; iCounter<arClass.length; iCounter++)
{
if (arClass[iCounter] == 'optional')
{
bOptional = true;
}
}

   if (bOptional && strValue.replace(/^\s*|\s*$/g, '') === '')
{
return true;
}

   return bValid;
}