how to do form validation in js code example

Example 1: html form validation

<form action="">
    <label for="name">Username</label>
    <input id="name" type="text" required />
    <label for="Email">Email</label>
    <!-- The required attribute will prompt the user to make sure  -->
    <!-- the fields are not empty, and that the email is formatted correctly -->
    <!-- if you want to use custom validation you should use regex in JavaScript -->
    <input id="Email" type="text" required />
</form>

Example 2: javascript form validation

<form name="myForm" action="/action_page.php" onsubmit="return validateForm()" 
method="post">

 Name: <input type="text" name="fname">

<input type="submit" value="Submit">

</form>