如何在输入表单中隐藏提示？

<input type="text" placeholder="请输入用户名">

<style>
    .hidden-label {
        display: none;
    }
</style>
<label for="username" class="hidden-label">用户名</label>
<input type="text" id="username">

<label for="username" id="username-label">用户名</label>
<input type="text" id="username">

<script>
    document.getElementById("username").addEventListener("focus", function() {
        document.getElementById("username-label").style.display = "none";
    });

    document.getElementById("username").addEventListener("blur", function() {
        if (this.value === "") {
            document.getElementById("username-label").style.display = "block";
        }
    });
</script>