function validate(){ var tos = document.getElementById('tos-check'); if(tos.checked){ document.getElementById('tos').submit(); }else{ var btn= document.getElementById('btn-sub'); var div = document.getElementById('div-content-form'); div.classList.remove("fadeInDown"); div.className += " shake"; btn.disabled = true; setTimeout (function(){ div.classList.remove("shake"); btn.disabled = false; }, 500); } } var element= document.getElementById('btn-sub'); element.addEventListener("click", validate, false);