JSFiddle - React, Tailwind, and code Playground

HTML

<input type="file" name="anexo" id="idAnexo" data-max-size="10000000" />

JavaScript

$(function () {
            $("input:file").change(function () {
                var fileInput = $(this);
                var maxSize = $(this).data('max-size');
                console.log(fileInput.get(0).files[0].size);

                //aqui a sua função normal
                if (fileInput.get(0).files.length) {
                    var fileSize = fileInput.get(0).files[0].size; // in bytes
                    if (fileSize > maxSize) {
                        alert('file size is more then' + maxSize + ' bytes');
                        return false;
                    } else {
                        alert('file size is correct- ' + fileSize + ' bytes');
                    }
                } else {
                    alert('choose file, please');
                    return false;
                }
            });
        });