原生js事件委托

var commontop = document.getElementById("commontop");
commontop.onclick = function(ev){
   var ev = ev || window.event;
   var target = ev.target || ev.srcElement;
   if(target.className.toLowerCase() == "h5navbox"){
      if(h5navcontent.style.display==='block'){
         h5navcontent.style.display = "none";
      }else{
         h5navcontent.style.display = "block";
      }
  }
};

target.className 目标元素的className;

类似jquery中的 commontop.on("click",".h5navbox",function(){...})