Use the condition with “” and NULL to check if value is empty. Throw a message whenever ua ser does not fill the text box value.
Example
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initialscale=1.0">
<title>Document</title>
<link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<script src="https://code.jquery.com/jquery-1.12.4.js"></script>
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
</head>
<body>
<form name="register" onsubmit="return checkingUserName()">
USERNAME: <input type="text" name="username">
<input type="submit" value="Save">
</form>
<script>
function checkingUserName() {
var username = document.forms["register"]["username"].value;
if (username == null || username == "") {
alert("Please enter> the username. Can’t be blank or empty !!!");
return false;
}
}
</script>
</body>
</html>To run the above program, save the file name “anyName.html(index.html)” and right click on the file. Select the option “Open with Live Server” in VS Code editor.
Output
This will produce the following output −
On clicking the Save button, you will get the following alert along with a message −
