Validate the form raised by the user because it can have blank values. So, validation is a must to authenticate users.


JavaScript library provides a way to validate the form on the client-side validation so data processing will be faster other than server-side validation. Most developers prefer JavaScript form validation.


So, in JavaScript, we can validate name, password, email, date, mobile numbers, and more fields.


index.php

<html>
    <head>
        <title>how to validate form in javascript?</title>
        <script>
            function validateform() {
                var user_name = document.myform.user_name.value;
                var user_address = document.myform.user_address.value;

                if (user_name == null || user_name == "") {
                    alert("User Name can't be blank");
                    return false;
                }
                if (user_address == null || user_address == "") {
                    alert("User Address can't be blank");
                    return false;
                }
            }
        </script>
    </head>
    <body>
        <form method = "post" name="myform" onsubmit="return validateform()" >
            <table width = "400" border = "0" cellspacing = "1" cellpadding = "2">
                <tr>
                    <td width = "100">User Name</td>
                    <td><input name = "user_name" type = "text" placeholder="User Name"></td>
                </tr>
                <tr>
                    <td width = "100">User Address</td>
                    <td><input name = "user_address" type = "text" placeholder="User Address"></td>
                </tr>
                <tr>
                    <td width = "100"> </td>
                    <td> </td>
                </tr>
                <tr>
                    <td width = "100"> </td>
                    <td>
                        <input name = "submit" type = "submit" value = "Add User">
                    </td>
                </tr>
            </table>
        </form>
    </body>
</html>

I hope it can help you...