WebPart form with JS submit preventDefault

I had to put the 

window.addEventListener("submit", handleFormSubmit);

In the method that build the form ... 

I had a first eventListener to load the form generated with JS : 

window.addEventListener("load", buildForm);

then in buildform() : 

const buildForm = () => {
    let requestForm = document.createElement('form');
    requestForm.setAttribute("class", "form-horizontal");
    requestForm.setAttribute("id", "requestForm");

    let parentFormDiv = document.getElementById("displayForm");
    parentFormDiv.appendChild(requestForm);

    ... building my stuff ...

    /**
     * Manage events on form submit : convert the form data in json and send to caml query
     */
    formElt.addEventListener("submit", handleFormSubmit);


};