SOURCE

document.querySelector('.options').addEventListener('click', function (evt) {
    if (evt.target.classList.contains('options')) {
      return;
    }
    var text = evt.target.innerHTML;
    //构造自定义事件
    var select = new CustomEvent('select', {
      detail: event.target.innerHTML,
      bubbles: true//允许冒泡被祖先元素监听到
    });
    evt.target.dispatchEvent(select)//把select事件抛出去
  })
  document.querySelector('.selector').addEventListener('select', function (evt){ 
    this.querySelector('.selected').innerHTML = evt.detail;
  })

<div class='selector'>
    <div class='selected'>啥都没选</div>
    <div class = 'options'>
      <div >1</div>
      <div >2</div>
      <div >3</div>
      <div >4</div>
      <div >5</div>
    </div>
  </div>