I want to add a length check to lastname input box and the firstname.To make it so the user can only enter an name between 3 to 20 characters in 'javascript'.
<form name="sign" onsubmit="" method="post" action="">
<div>
<p>It must be between 3 to 20 characters</p>
<input type="text" required placeholder="Enter your first name">
</div>
<div>
<input type="text" required placeholder="Enter your last name">
</div>
<div>
<input id="age" required name="data" type="number" placeholder="Enter your age">
</div>
<div>
<input type="text" required placeholder="Enter your email">
</div>
<div>
<input type="submit" required value="Submit">
</div>
</form>
