Simple Example for Submit Validation

HTML

<script type="text/javascript">
function checkValues()
{
    var item = document.getElementById('username');
    var error = false;

    if(item.value.length < 5)
    {
        error = true;
        item.style.backgroundColor = "#FF0000";
    }
    else
    {
        item.style.backgroundColor = "#FFFFFF";
    }


//    if(error === false) {
      // wenn alles valide, submit()
//        document['UmfragenForm'].submit();
//    }
}
    
</script>

<input type="text" id="username" name="username" placeholder="Username"><br>
<button type="submit" onClick="checkValues()">Submit</button>