philphil

const re = /(.+)\[(.+)\]\[(.+)\]/;
const formData = new FormData(drawingForm);
const result = {};
for (const [key, value] of Object.entries(formData)) {
    const matches = key.match(re);
    if (!matches) { continue }
    const [, k1, k2, k3] = matches;
    ((result[k1] ??= {})[k2] ??= {})[k3] = value;
}
console.log(result); // тут валидация