<form id ="login-form">
    <span id="name"></span><br>
    <input id="username-input" type="text" placeholder="USERNAME">
</form>

<script>
$(function () {
    $("#username-input").keydown(function() {
    function addRemoveUsername () {
        var inputChecker = document.getElementById("username-input");
        if (inputChecker.value == "") {
            document.getElementById("name").innerHTML = "";
        } else {
            document.getElementById("name").innerHTML = "USERNAME";
        }
    }
    addRemoveUsername();
    });
});
</script>