대상객체.addEventListener( click, 함수명);

<div id="cols">
    <button class="btn">A</button>
    <button class="btn">B</button>
    <button class="btn">C</button>
</div>

<script>
    var cols = document.querySelectorAll("#cols .btn");

    for( var i=0; i<cols.length; i++){
        cols[i].addEventListener("click", fn_name);        
    }
    cols[1].style.color = "red";

    function fn_name(){
        window.alert(this.innerHTML);
    }
</script>

const tit = document.querySelector("h1");
tit.addEventListener("click", fun_name);

//반대
tit.removeEventListener("click", fun_name);

function fun_name(){
 console.log('성공!!');
}