clipboard.js

var btn = document.getElementById("copy-button");
btn.addEventListener("click", clickHandler, false);

function clickHandler(e) {
  var clip = new ClipboardEvent("copy");
  clip.clipboardData.setData("text/plain", "foo");
  clip.clipboardData.setData("text/html", "<b>foo</b>");

  // CRITICAL: Must call `preventDefault();` to get this data into the system/desktop clipboard!!!
  clip.preventDefault();

  e.target.dispatchEvent(clip);
}

fix clip.setData to clip.clipboardData.setData() :-)

Good catch, thanks! Fixed.