JSFiddle - React, Tailwind, and code Playground

HTML

<form id="anexarArquivos" enctype="multipart/form-data"></form>

JavaScript

var formAnexo = null;
alert(document.getElementById('anexarArquivos'));
if(document.getElementById('anexarArquivos').getAttribute('enctype') == "multipart/form-data") {

    formAnexo = new FormData(document.getElementById('anexarArquivos'));
    alert(formAnexo === undefined);
}