<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
    </head>
    <body>
        <button class='up'>销量升序</button>
        <button class='down'>销量降序</button>
        <ul></ul>

        <script>
            var cups = [
                { type: 1, price: 100, color: 'black', sales: 3000, name: '牛客logo马克杯' },
                { type: 2, price: 40, color: 'blue', sales: 1000, name: '无盖星空杯' },
                { type: 4, price: 60, color: 'green', sales: 200, name: '老式茶杯' },
                { type: 3, price: 50, color: 'green', sales: 600, name: '欧式印花杯' }
            ]
            var ul = document.querySelector('ul');
            var upbtn = document.querySelector('.up');
            var downbtn = document.querySelector('.down');
            // 补全代码
           upbtn.onclick = function(){
                ul.innerHTML = ''
                cups.sort(function(a,b){
                    return a.sales - b.sales;
                })
              
                for(let i =0;i <cups.length;i++){
                    let li = document.createElement('li');
                    li.innerHTML  = `${cups[i].name}`
                    ul.appendChild(li)
                }
            }
            downbtn.onclick = function(){
                ul.innerHTML = '';
                cups.sort(function(a,b){
                    return b.sales - a.sales;
                })
              
                for(let i =0;i <cups.length;i++){
                    let li = document.createElement('li');
                    li.innerHTML  = `${cups[i].name}`
                    ul.appendChild(li)
                }
            }
        </script>
    </body>
</html>