<button class="red">red</button>     <button></button>

 let arr=[1,3,4,34];
   let res= arr.filter(item=>{
        return item>30;
    });
    console.log(res);
   let btns= document.querySelectorAll("button");
   btns=Array.prototype.filter.call(btns,item=>{
//    btns=[].filter.call(btns,item=>{
       return item.hasAttribute("class");
   });
   console.log(btns);