code: function simpleSelector(sources, callback) {
  
    var options = crel('select', {
      style: 'margin: 0.5rem'
    }, sources.map(function(source) {
      return crel('option', {id: source.id, value: source.id}, source.name);
    }));
  
    var selector = crel('div',
      {
        style: 'position: absolute; padding: 1rem; z-index: 999999; background: #ffffff; width: 100%; font-family: \'Lucida Sans Unicode\', \'Lucida Grande\', sans-serif; box-shadow: 0px 2px 4px #dddddd;'
      },
      crel('label', { style: 'margin: 0.5rem' }, 'Share screen:'),
      options,
      crel('span', { style: 'margin: 0.5rem; display: inline-block' },
        button('Share', function() {
          close();
          var selected = sources.filter(function(source) {
            return source && source.id === options.value;
          })[0];
          return callback(null, options.value, { title: selected.name });
        }),
        button('Cancel', close)
      )
    );
  
    function button(text, fn) {
      var button = crel('button', {
        style: 'background: #555555; color: #ffffff; padding: 0.5rem 1rem; margin: 0rem 0.2rem;'
      }, text);
      button.addEventListener('click', fn);
      return button;
    }
  
    function close() {
      document.body.removeChild(selector);
    }
  
    document.body.appendChild(selector);
  }
docs: This is just a simple default screen selector implementation