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Bootstrap 5: Error when showing dropdown via JavaScript

I’m trying to show a dropdown via JS. Unfortunately it seems like there’s a bug in Bootstrap 5. In this example code, showing the modal works, but showing the dropdown throws an exception: Uncaught TypeError: Cannot read property 'classList' of undefined at _e.show (dropdown.js:140)

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css">
</head>

<body>

<div id="testDropdown" class="dropdown">
    <button class="btn btn-secondary dropdown-toggle" type="button" data-bs-toggle="dropdown">
        Dropdown button
    </button>
    <ul class="dropdown-menu">
        <li><a class="dropdown-item" href="#">Action</a></li>
        <li><a class="dropdown-item" href="#">Another action</a></li>
        <li><a class="dropdown-item" href="#">Something else here</a></li>
    </ul>
</div>

<div id="testModal" class="modal" tabindex="-1">
    <div class="modal-dialog">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title">Modal title</h5>
                <button type="button" class="btn-close" data-bs-dismiss="modal"></button>
            </div>
            <div class="modal-body">
                <p>Modal body text goes here.</p>
            </div>
        </div>
    </div>
</div>

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js"></script>

<script>

    let testModal = document.getElementById("testModal");
    //new bootstrap.Modal(testModal).show(); //works

    let testDropdown = document.getElementById("testDropdown");
    new bootstrap.Dropdown(testDropdown).show(); //doesnt work

</script>

</body>
</html>

Am I doing something wrong or is this a bug?

Thanks in advance.

Answer

The element should be the dropdown-trigger instead of the parent dropdown…

<div class="dropdown">
    <button class="btn btn-secondary dropdown-toggle" id="testDropdown" type="button" data-bs-toggle="dropdown"> Dropdown button </button>
    <ul class="dropdown-menu">
        <li><a class="dropdown-item" href="#">Action</a></li>
        <li><a class="dropdown-item" href="#">Another action</a></li>
        <li><a class="dropdown-item" href="#">Something else here</a></li>
    </ul>
</div>

Demo