document.addEventListener("DOMContentLoaded", ()=>{ document.getElementById("h1").addEventListener("click", (e) => { alert("Hello"); }, false); }); function dbiSize(){ var dbi = document.querySelectorAll('p'); if (dbi.length == 0){ alert('p??????????????'); }else { for (let i of dbi){ i.style.fontSize = '200%'; } } } window.addEventListener("load", function(e){ document.body.addEventListener("click",dbiSize); })