js check form required code example

Example 1: name validation html

<input type="text" pattern="[a-zA-Z'-'\s]*">

Example 2: javascript login validation

<script language = "JavaScript">
        function validate() {
            var username = document.getElementById("username").value;
            var password = document.getElementById("password").value;
            if (username == null || username == "") {
                alert("Please enter the username.");
                return false;
            }
            if (password == null || password == "") {
                alert("Please enter the password.");
                return false;
            }
            alert('Login successful');
            
        } 
</script>

Example 3: using javascript to validation email before next field

/^[a-zA-Z0–9.!#$%&’*+\/=?^_`{|}~-]+@[a-zA-Z0–9](?:[a-zA-Z0–9-]{0,61} [a-zA-Z0–9])?(?:\.[a-zA-Z0–9](?:[a-zA-Z0–9-]{0,61}[a-zA-Z0–9])?)*$/