How to run this script after loading the page

Question

const dropzoneBtnList = document.querySelectorAll(".custom-dropzones-wrapper .dropzone-btn");       
     dropzoneBtnList.forEach((dropzoneBtn) => {
    dropzoneBtn.addEventListener('click',function(e){
    e.currentTarget.classList.toggle("active");
    })
})

How to run this script only after loading the webpage