JS中querySelectorAll的作用

//外部页切换
    var clickme=document.getElementById(‘navbox‘).getElementsByTagName(‘button‘);
    var box=document.getElementById(‘itembox‘).querySelectorAll(‘.boxStyle‘);
    for(var i=0;i<clickme.length;i++){
        clickme[i].index=i;
        clickme[i].onclick=function(){
            for(var i=0;i<clickme.length;i++){
                clickme[i].className=‘navbtn‘;
                box[i].style.display=‘none‘;
            }
            this.className=‘navbtn active‘;
            box[this.index].style.display=‘block‘;
        }
    }
    //内部页切换
    var databox=document.getElementById(‘b1‘).getElementsByTagName(‘div‘);
    var message=document.getElementById(‘b2‘).getElementsByTagName(‘div‘);
    for(var i=0;i<databox.length;i++){
        databox[i].index=i;
        databox[i].onclick=function(){
            for(var i=0;i<databox.length;i++){
                databox[i].className=‘littlebox‘;
                message[i].style.display=‘none‘;
            }
            this.className=‘littlebox actives‘;
            message[this.index].style.display=‘block‘;
        }
    }