Code snippet to copy text to clipboard (doesn't work from a Chrome extension background.js)

test.js

var text = 'Hello world';

var buffer = document.createElement('buffer');
document.body.appendChild(buffer);
buffer.value = text;
buffer.focus();
buffer.selectionStart = 0;
buffer.selectionEnd = buffer.value.length;
if (!document.execCommand('copy')) {
  console.log('Couldn\'t copy from buffer');
}