Object to FormData

serialize.ts

import "@total-typescript/ts-reset";

function isUndefined(value: unknown): value is undefined {
  return typeof value === "undefined";
}

function isNull(value: unknown): value is null {
  return value === null;
}

function isNil(value: unknown): value is undefined | null {
  return isNull(value) || isUndefined(value);
}

function isDate(value: unknown): value is Date {
  return value instanceof Date;
}

function isBlob(value: unknown): value is Blob {
  return value instanceof Blob;
}

export type Primitives =
  | undefined
  | null
  | string
  | boolean
  | number
  | Date
  | Blob;

export type SerializableObject = {
  [key: string]: Primitives | Array<Primitives>;
};

export type Options = {
  dateFormatter: (date: Date) => string;
};

const defaultOptions: Options = {
  dateFormatter: (date: Date) => date.toISOString(),
};

function serializePrimitives(
  value: Omit<Primitives, "null" | "undefined">,
  options: Options
): Blob | string {
  if (isDate(value)) {
    return options.dateFormatter?.(value);
  }

  if (isBlob(value)) {
    return value;
  }

  return value.toString();
}

export function serialize(
  object: SerializableObject,
  options: Options = defaultOptions
) {
  const formData = new FormData();

  for (const [key, value] of Object.entries(object)) {
    ([] as Array<Primitives>)
      .concat(value)
      .filter((v) => !isNil(v))
      .forEach((v) => {
        formData.append(key, serializePrimitives(v, options));
      });
  }

  return formData;
}