A function to convert FormData into an object, supporting multiple values per key using arrays.

form-data-to-object.ts

export default async function formDataToObject(
  formData: Promise<FormData> | FormData,
): Promise<Record<string, unknown>> {
  const object: Record<string, unknown> = {};
  for (const [key, value] of await Promise.resolve(formData)) {
    const property = object[key];
    if (property === undefined) {
      object[key] = value;
    } else if (Array.isArray(property)) {
      property.push(value);
    } else {
      object[key] = [property, value];
    }
  }
  return object;
}