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Lessons JavaScript HTML Web Form Validation Bookmark and Share
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One of the most important uses of JavaScript is to use it to validate or check the web form data for errors before submitting the same to the web server.

The process of checking that a from has been filled in correctly or not before it is submitted to the web server is called "Form Validation". HTML form validation through JavaScript on the client side helps to reduce unnecessary burdon on the web server.

Client side form validation is an important part of any website that collects and stores user data. From the perspective of a web developer, internet users tend to make mistakes and it is the responsibility of a web developer to deal with such errors.

The following example demonstrates form validation through JavaScript:

<script type="text/JavaScript">
function validateForm()
var name=document.forms["form1"]["name"].value;
if (name == null || name == "")
alert("Name field cannot be empty");
return false;
} </script>

<form name="form1" action="JavaScript_form_validation.php" onsubmit="return validateForm()" method="post">
First name: <input type="text" name="name">
<input type="submit" value="Submit">


The above code defines a function named validateForm() in the header section of the web page, that validates the form. The form elements are accessed through the document.forms array. Also note the use of the onsubmit="return validateForm()" attribute of the above form. This attribute calls the function validateForm() when the user clicks on the submit button.

If the data checks fail the function alerts the user of the error and the function ends with the following statement:

return false;

We have to end our validation function with the above statement if we want that the data must not be submitted to the web server.

Next >>> Lesson No. 46: HTML Document Object Model

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