How can I copy to clipboard in HTML5 without using flash?

I want to use a copy-to-clipboard function in HTML5, but without using flash. Is it possible? How?

I tried to implement a copy-to-clipboad function with JavaScript, but it is not working:

function Copytoclipboard() {
    var body = document.body,
        range, sel;
    if (document.createRange && window.getSelection) {
        range = document.createRange();
        sel = window.getSelection();
        sel.removeAllRanges();
        try {
            range.selectNodeContents(el);
            sel.addRange(range);
            document.execCommand('Copy');
        } catch (e) {
            range.selectNode(el);
            sel.addRange(range);
            document.execCommand('Copy');
        }
    } else if (body.createTextRange) {
        range = body.createTextRange();
        range.moveToElementText(el);
        range.select();
        range.execCommand('Copy');
    }
}

You can use the HTML5 clipboard api http://www.htmlgoodies.com/html5/other/working-with-clipboard-apis-in-html5-web-apps.html#fbid=eh9tM7GHJWF

But do note that not all browsers fully support it as of now: http://caniuse.com/#feat=clipboard

UPDATE: This solution now works in the current version of all major browsers!

function copyText(text){
  function selectElementText(element) {
    if (document.selection) {
      var range = document.body.createTextRange();
      range.moveToElementText(element);
      range.select();
    } else if (window.getSelection) {
      var range = document.createRange();
      range.selectNode(element);
      window.getSelection().removeAllRanges();
      window.getSelection().addRange(range);
    }
  }
  var element = document.createElement('DIV');
  element.textContent = text;
  document.body.appendChild(element);
  selectElementText(element);
  document.execCommand('copy');
  element.remove();
}


var txt = document.getElementById('txt');
var btn = document.getElementById('btn');
btn.addEventListener('click', function(){
  copyText(txt.value);
})

<input id="txt" />
<button id="btn">Copy To Clipboard</button>

Note: Trying to use this solution to copy an empty string or a string that is only whitespace will not work.

ALTERNATE, SIMPLIFIED SOLUTION

This alternate solution has been tested in Chrome, Safari, and Firefox.

const txt = document.querySelector('#txt')
const btn = document.querySelector('#btn')

const copy = (text) => {
  const textarea = document.createElement('textarea')
  document.body.appendChild(textarea)
  textarea.value = text
  textarea.select()
  document.execCommand('copy')
  textarea.remove()
}

btn.addEventListener('click', (e) => {
  copy(txt.value)
})

<input id="txt" />
<button id="btn">Copy</button>

Note: This solution will not copy an empty string, but it will copy whitespace.

It's not working because it requires a user interaction such as click. Otherwise, document.execCommand will not work. You also might wanna check clipboard.js, it's a super easy library to copy text to clipboard that doesn't require Flash.