JavaScript Form Validation : quick and easy!

Using client side JavaScript is an efficient way to validate the user input in web forms. When there are many fields in the form, the JavaScript validation becomes too complex.

The JavaScript class presented here makes the form validations many times easier.

How to add JavaScript Form Validation quickly

First, download the JavaScript form validation script here. The zip file contains the javascript file, examples.

The script has a catalog of almost all the common validation types built-in.

The idea is to create a set of “validation descriptors” associated with each element in a form. The “validation descriptor” is nothing but a string specifying the type of validation to be performed.

Each field in the form can have zero one or more validations. For example, you can have an input field that should not be empty, should be less than 25 chars and should be alpha-numeric.

In other words, in order to validate a field, you just associate a set of validation descriptors for each input field in the form.

Using the form validation script

Include gen_validatorv4.js in your html file just before closing the HEAD tag


<script src="gen_validatorv4.js" type="text/javascript"></script>
</head>

Just after defining your form, create a Validator() object passing the name of the form


<form id='myform' action="">
 <!----Your input fields go here -->
 </form>

<script type="text/javascript">
 var frmvalidator  = new Validator("myform");
                     //where myform is the name/id of your form

Now, add the validations required


frmvalidator.addValidation("FirstName","req","Please enter your First Name");

The format of the addValidation() function is:


frmvalidator.addValidation(Field Name, Validation Descriptor, Error String);

See below for the complete list of validation descriptors. The third parameter ( Error string ) is optional. You can add any number of validations to a field.


frmvalidator.addValidation("FirstName","req","Please enter your First Name");
frmvalidator.addValidation("FirstName","maxlen=40",
                                          "Max length for FirstName is 40");

Example

Here is a complete example:


<form action="" id="myform" >
<p>
	<label for='FirstName'>First Name:</label>
	<input type="text" id="FirstName" name="FirstName" />
</p>
<p>
	<label for='LastName'>Last Name:</label>
	<input type="text" id="LastName" name="LastName" />
</p>
<p>
	<label for='EMail'>EMail:</label>
	<input type="text" id="EMail" name="EMail" />
</p>
<p>
	<label for='Phone'>Phone:</label>
	<input type="text" id="Phone" name="Phone" />
</p>
<p>
	<label for='Address'>Address:</label>
	<textarea cols="20" rows="5" id="Address" name="Address"></textarea>
</p>
<p>
	<label for='Country'>Country:</label>
	<select id="Country"  name="Country">
        <option value="000" selected="selected">[choose yours]</option>
        <option value="008">Albania</option>
        <option value="012">Algeria</option>
        <option value="016">American Samoa</option>
        <option value="020">Andorra</option>
        <option value="024">Angola</option>
        <option value="660">Anguilla</option>
        <option value="010">Antarctica</option>
        <option value="028">Antigua And Barbuda</option>
        <option value="032">Argentina</option>
        <option value="051">Armenia</option>
        <option value="533">Aruba</option>
	</select>
</p>
<p>
	<input type="submit" name="submit" value="Submit">
</p>
</form>

<script  type="text/javascript">
 var frmvalidator = new Validator("myform");
 frmvalidator.addValidation("FirstName","req","Please enter your First Name");
 frmvalidator.addValidation("FirstName","maxlen=20",
		"Max length for FirstName is 20");

 frmvalidator.addValidation("LastName","req");
 frmvalidator.addValidation("LastName","maxlen=20");

 frmvalidator.addValidation("Email","maxlen=50");
 frmvalidator.addValidation("Email","req");
 frmvalidator.addValidation("Email","email");

 frmvalidator.addValidation("Phone","maxlen=50");
 frmvalidator.addValidation("Phone","numeric");

 frmvalidator.addValidation("Address","maxlen=50");
 frmvalidator.addValidation("Country","dontselect=000");

</script>

Some Additional Notes

The form validators should be created only after defining the HTML form (only after the tag. )
Your form should have a distinguished name. If there are more than one form in the same page, you can add validators for each of them. The names of the forms and the validators should not clash.
You can’t use the javascript onsubmit event of the form if it you are using this validator script. It is because the validator script automatically overrides the onsubmit event. If you want to add a custom validation, see the section below

Adding a custom validation

If you want to add a custom validation, which is not provided by the validation descriptors, you can do so. Here are the steps:

Create a javascript function which returns true or false depending on the validation


function DoCustomValidation()
{
  var frm = document.forms["myform"];
  if(frm.pwd1.value != frm.pwd2.value)
  {
    sfm_show_error_msg('The Password and verified password does not match!',frm.pwd1);
    return false;
  }
  else
  {
    return true;
  }
}

sfm_show_error_msg() function displays the error message in your chosen style. The first parameter is the error message and the second parameter is the input object.

Associate the validation function with the validator object.

frmvalidator.setAddnlValidationFunction("DoCustomValidation");

The custom validation function will be called automatically after other validations.

If you want to do more than one custom validations, you can do all those validations in the same function.


function DoCustomValidation()
{
  var frm = document.forms["myform"];
  if(false == DoMyValidationOne())
  {
    sfm_show_error_msg('Validation One Failed!');
    return false;
  }
  else
  if(false == DoMyValidationTwo())
  {
    sfm_show_error_msg('Validation Two Failed!');
    return false;
  }
  else
  {
    return true;
  }
}

where DoMyValidationOne() and DoMyValidationTwo() are custom functions for validation.

Clear All Validations

In some dynamically programmed pages, it may be required to change the validations in the form at run time. For such cases, a function is included which clears all validations in the validator object.


frmvalidator.clearAllValidations();

This function call clears all validations you set.

Set focus on validation failure

By default, if there is a validation error, the focus is set on the input element having the error. You can disable this behavior by calling:


frmvalidator.EnableFocusOnError(false);

Validation Descriptors

Here is the list of all validation descriptors:

required or req

The field should not be empty.

Note that this validation if for fields like Textbox and multi-line text box. For ‘selections’ like drop down and radio group, use an appropriate validation like ‘dontselect’ or ‘selone_radio’.

maxlen=??? or maxlength=???

Limits the length of the input. For example, if the maximum size permitted is 25, give the validation descriptor as “maxlen=25”

minlen=??? or minlength=???

Checks the length of the entered string to the required minimum. Example “minlen=5”

alphanumeric or alnum

The input can contain English alphabetic or numeric characters only. (Note that space or punctuation also are not allowed since those characters are not alpha-numeric)

alphanumeric_space alnum_s

Allows only English alphabetic, numeric and space characters

num numeric

Allow numbers only

alpha alphabetic

Allow only English alphabetic characters.

alpha_s alphabetic_space

Allows alphabetic and space characters

email

Validates the field to be a proper email address. (Note, However that the validation can’t check whether the email address exists or not)

lt=??? OR lessthan=???

Verify the data to be less than the value passed. Valid only for numeric fields. Example: if the value should be less than 1000 give validation description as “lt=1000”

gt=??? OR greaterthan=???

Verify the data to be greater than the value passed. Valid only for numeric fields. Example: if the value should be greater than 10 give validation description as “gt=10”

regexp=???

Match the input with a regular expression. Example: “regexp=^[A-Za-z]{1,20}$” allow up to 20 alphabetic characters.

dontselect=??

This validation descriptor is valid only for drop down lists. The drop down select list boxes usually will have one item saying ‘Select One’ (and that item will be selected by default). The user should select an option other than this ‘Select One’ item. If the value of this default option is ‘000’, the validation description should be “dontselect=000”

Dropdown box with default selected

Drop down list source

dontselectchk=??

This validation descriptor is only for check boxes. The user should not select the given check box. Provide the value of the check box instead of ?? For example, dontselectchk=on

shouldselchk=??

This validation descriptor is only for check boxes. The user should select the given check box. Provide the value of the check box instead of ?? For example, shouldselchk=on

selone_radio

One of the radio buttons should be selected. Example:

chktestValidator.addValidation("Options","selone");

Compare two input elements

eqelmnt=???

Compare two input elements. For example: password and confirm password. Replace ??? with the name of the other input element. Example:


frmvalidator.addValidation("confpassword","eqelmnt=password",
 "The confirmed password is not same as password");

neelmnt=???

The value should not be equal to the other input element Example:


frmvalidator.addValidation("password","neelmnt=username",
"The password should not be same as username");

ltelmnt=???

The input should be less than the other input. Give the name of the other input instead of ???

leelmnt=???

The input should be less than or equal to the other input. Give the name of the other input instead of ???

gtelmnt=???

The input should be greater than the other input. Give the name of the other input instead of ???

geelmnt=???

The input should be greater than or equal to the other input. Give the name of the other input instead of ???

Go to the second part of this post to learn about the advanced features of this validation script.