Closure in loop

HTML

<a href="#" id="1_Btn" class="button">1</a>
<a href="#" id="2_Btn" class="button">2</a>
<a href="#" id="3_Btn" class="button">3</a>

JavaScript

var buttons = document.querySelectorAll(".button");
console.log(buttons);
function Btn_check(){
    for(var i=0; i<buttons.length; i++) {
      buttons[i].onclick = (function(n) {
      	return function() {
          alert(buttons[n].getAttribute("id"));
        }
      })(i);

    }
}

setInterval(Btn_check(), 1000/30);