HTML

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <link
      rel="icon"
      href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 100 100%22><text y=%22.9em%22 font-size=%2290%22>🎉</text></svg>"
    />
    <title>How to paste text</title>
  </head>
  <body>
    <h1>How to paste text</h1>
    <p>
      <button type="button">Paste</button>
    </p>
    <textarea></textarea>
  </body>
</html>

CSS


        :root {
  color-scheme: dark light;
}

html {
  box-sizing: border-box;
}

*,
*:before,
*:after {
  box-sizing: inherit;
}

body {
  margin: 1rem;
  font-family: system-ui, sans-serif;
}

button {
  display: block;
}

JS


        const pasteButton = document.querySelector('button');

pasteButton.addEventListener('click', async () => {
  try {
    const text = await navigator.clipboard.readText()
    document.querySelector('textarea').value += text;
    console.log('Text pasted.');
  } catch (error) {
    console.log('Failed to read clipboard. Using execCommand instead.');
    document.querySelector('textarea').focus();
    const result = document.execCommand('paste')
    console.log('document.execCommand result: ', result);
  }
});