xe-clipboard

npm install xe-clipboard

<script src="https://cdn.jsdelivr.net/npm/xe-clipboard"></script>

<button id="btn1">Copy</button>

document.getElementById('btn1').addEventListener('click', function (evnt) {
  // 由于浏览器的安全机制，操作剪贴板必须在事件之内才能有效
  if (XEClipboard.copy('Copy this content to the clipboard.')) {
    alert('Copy success.')
  } else {
    alert('The browser is not supported.')
  }
})