JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <div id="Q01">
        <p>Some text</p>
    </div>
    <div id="Q02">
        <p>Some text</p>
    </div>
    <div id="Q03">
        <p>Some text</p>
    </div>

        <label for="number">Number of DIVs:</label>
        <input type="number" name="result" id="number">
</div>

JavaScript

alert(  document.querySelectorAll('[id^=Q]').length   );