手写JS 实现事件委托

 <ul id="list">
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
 </ul>

let ul = document.querySelector('#list');

ul.addEventListener('click', function(e){
    let target = e.target;

    while( target.tagName !== 'LI' ){
           if ( target.tagName === 'UL' ){
                target = null;
                break;
           }

           target = target.parentNode;
    }

    if ( target ){
        console.log('你点击了ui里的li')
    }
})