<input id="foo" type="text" value="https://chupai.github.io/">
<button class="btn">cut</button>

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  overflow: hidden;
}

console.clear();

const clipboard = new ClipboardJS('.btn', {
  target() {
    return document.querySelector('#foo');
  }
});