Javascript Validations
How to use JavaScript to validate an HTML form. We have discussed the following HTML Form Validation topics with examples:

1. Required fields 
2. Letters only
3. Name fields
4. Numbers only
5. Email validation
6. Select from list
7. Password Validations. etc..
Required Field Validation :
<html>
<head>
<title>Required Field Validation </title>

<script type='text/javascript'>
function notEmpty(elem, helperMsg){
if(elem.value.length == 0){
alert(helperMsg);
elem.focus();
return false;
}
return true;
}
</script>

</head>
<body>
 
<form>
Required Field: <input type='text' id='req1'/>
<input type='button' onclick="notEmpty(document.getElementById('req1'), 'Please Enter a any value or name')" value='Check Field' />
</form>

</body>
</html>
Output :
Required Field:
Letters only :
<html>
<head>
<title>Letters only</title>
 
<script type='text/javascript'>
function isAlphabet(elem, helperMsg){
var alphaExp = /^[a-zA-Z]+$/;
if(elem.value.match(alphaExp))
{
return true;
}
else
{
alert(helperMsg);
elem.focus();
return false;
}
}
</script>

</head>
<body>

<form>
Letters Only: <input type='text' id='letters'/>
<input type='button' onclick="isAlphabet(document.getElementById('letters'), 'Please enter letters only.')" value='Check Field' />
</form>

</body>
</html>
Output :
Letters Only:
Name Field Validation :
<html>
<head>
<title>Name fields</title>

<script type="text/javascript">
function validateForm()
{
var x=document.forms["myForm"]["fname"].value;
if (x==null || x=="")
  {
  alert("Please enter first name.");
  return false;
  }
 var y=document.forms["myForm"]["lname"].value;
 if(y==null || y=="")
 {
 alert("Please enter last name."); 
 }
}
</script>

<style type="text/css">
.lable{ 
font-family:Arial, Helvetica, sans-serif; 
font-size:13px; 
font-style:italic; 
margin:5px 0px; 
font-weight:bold; 
clear:both;
}
.cus_form{ 
height:30px; 
padding:0px 1px; 
margin:2px 0px 10px;
} 
.cus_btn{
padding:7px 15px; 
border-radius:2px; 
background:#09C; 
color:#FFF; 
margin-left:10px;
}
.cus_btn:hover{ background:#069;}
</style>

</head>
<body>

<form name="myForm" action="" onSubmit="return validateForm()" method="post">
<label class="lable">First Name</label>
<input type="text" class="cus_form" name="fname" /><br>
<label class="lable">Last Name</label>
<input type="text" class="cus_form" name="lname" /><br>
<input type="submit" class="cus_btn" value="Submit">
</form>

</body>
</html>
Output :


Numbers Only :
<html>
<head>
<title>Numbers Only</title>
 
<style type="text/css">
.lable{ 
font-family:Arial, Helvetica, sans-serif; 
font-size:13px; 
font-style:italic; 
margin:5px 0px; 
font-weight:bold; 
clear:both;
}
.cus_form{ 
height:30px; 
padding:0px 1px; 
margin:2px 0px 10px;
} 
.cus_btn{
padding:7px 15px; 
border-radius:2px; 
background:#09C; 
color:#FFF; 
margin-left:10px;
}
.cus_btn:hover{ background:#069;}
</style>
 
<script type='text/javascript'>
function isNumeric(elem, helperMsg){
var numericExpression = /^[0-9]+$/;
if(elem.value.match(numericExpression)){
return true;
}else{
alert(helperMsg);
elem.focus();
return false;
}
}
</script>

</head>
<body>
 
 
<form>
<label class="lable">Numbers Only :</label>
 <input type='text' id='numbers' class="cus_form"/>
<input type='button' onclick="isNumeric(document.getElementById('numbers'), 'Please Enter Numbers Only')" class="cus_btn" value='Check Field' />
</form>

</body>
</html>
Output :
Email Validations :
	
<html>
<head>
<title>Email Validations</title>
 
<style type="text/css">
.lable{ 
font-family:Arial, Helvetica, sans-serif; 
font-size:13px; 
font-style:italic; 
margin:5px 0px; 
font-weight:bold; 
clear:both;
}
.cus_form{ 
height:30px; 
padding:0px 1px; 
margin:2px 0px 10px;
} 
.cus_btn{
padding:7px 15px; 
border-radius:2px; 
background:#09C; 
color:#FFF; 
margin-left:10px;
}
.cus_btn:hover{ background:#069;}
</style>
 
<script type="text/javascript">
function validateForm()
{
var x=document.forms["myForm"]["email"].value;
var atpos=x.indexOf("@");
var dotpos=x.lastIndexOf(".");
if (atpos<1 || dotpos<atpos+2 || dotpos+2>=x.length)
  {
  alert("Not a valid e-mail address");
  return false;
  }
}
</script>
 
<form name="myForm" action="" onSubmit="return validateForm();" method="post">
<label class="lable">Email :</label> 
<input type="text" name="email" class="cus_form">
<input type="submit" class="cus_btn" value="Submit">
</form>
 
</body>
</html>
Output :
Select From List :
<html>
<head>
<title>Select Box Validation</title>
 
<style type="text/css">
.lable{ 
font-family:Arial, Helvetica, sans-serif; 
font-size:13px; font-style:italic; 
margin:5px 0px; 
font-weight:bold; 
clear:both;
}
.cus_form{ 
height:30px; 
padding:0px 1px; 
margin:2px 0px 10px;
} 
.cus_btn{
padding:7px 15px; 
border-radius:2px; 
background:#09C; 
color:#FFF; 
margin-left:10px;
}
.cus_btn:hover{ background:#069;}
</style>
 
<script type="text/javascript">
function madeSelection(elem, helperMsg){
if(elem.value == "Please Choose"){
alert(helperMsg);
elem.focus();
return false;
}else{
return true;
}
}
</script>
</head>
<body>
<form>
  <label class="lable">Selection :</label>
  <select id='selection' class="cus_form">
    <option>Please Choose</option>
    <option>Google</option>
    <option>Bing</option>
    <option>Yahoo</option>
  </select>
  <input type='button' class="cus_btn" onClick="madeSelection(document.getElementById('selection'), 'Please Choose Something')" value='Check Field' />
</form>
 
 
</body>
</html>
Output :
Password Validations :
<html>
<head>
<title>Password Validations</title>
 
<style type="text/css">
.lable{ 
font-family:Arial, Helvetica, sans-serif; 
font-size:13px; font-style:italic; 
margin:5px 0px; 
font-weight:bold; 
clear:both;
}
.cus_form{ 
height:30px; 
padding:0px 1px; 
margin:2px 0px 10px;
} 
.cus_btn{
padding:7px 15px; 
border-radius:2px; 
background:#09C; 
color:#FFF; 
margin-left:10px;
}
.cus_btn:hover{ background:#069;}
</style>
 
<script type="text/javascript">
function matchpass(){
var firstpassword=document.f1.password.value;
var secondpassword=document.f1.password2.value;
 
if(firstpassword==secondpassword){
return true;
}
else{
alert("password must be same!");
return false;
}
}
</script>

</head>
<body>
 
<form name="f1" action="" onsubmit="return matchpass()">
<label class="lable">Password :</label>
<input type="password" name="password" class="cus_form" /><br/>
 
<label class="lable">Re-enter Password :</label>
<input type="password" name="password2" class="cus_form"/><br/>
<input type="submit" class="cus_btn">
</form>
 
</body>
</html>
Output :