https://josephkhan.me/javascript-copy-clipboard-safari/

copy-text.js

function copyToClipboard(textToCopy) {
  var textArea;

  function isOS() {
    //can use a better detection logic here
    return navigator.userAgent.match(/ipad|iphone/i);
  }

  function createTextArea(text) {
    textArea = document.createElement('textArea');
    textArea.readOnly = true;
    textArea.contentEditable = true;
    textArea.value = text;
    document.body.appendChild(textArea);
  }

  function selectText() {
    var range, selection;

    if (isOS()) {
      range = document.createRange();
      range.selectNodeContents(textArea);
      selection = window.getSelection();
      selection.removeAllRanges();
      selection.addRange(range);
      textArea.setSelectionRange(0, 999999);
    } else {
      textArea.select();
    }
  }

  function copyTo() {
    document.execCommand('copy');
    document.body.removeChild(textArea);
  }

  createTextArea(textToCopy);
  selectText();
  copyTo();
}