var sidebar = document.getElementById('显示或隐藏的元素');

var overlay = document.getElementById('div元素id');

var yyy = document.getElementById('按钮元素id');


function 函数名() {
    sidebar.classList.toggle('active');
    overlay.style.display = sidebar.classList.contains('active') ? 'block' : 'none';
    sidebar.style.display = sidebar.classList.contains('active') ? 'block' : 'none';
 
    yyy.innerHTML = sidebar.classList.contains('active') ? 'X' : '≡';
}