http.ts

import { RequestInit } from 'next/dist/server/web/spec-extension/request';

type DefaultOptions = {
  baseUrl: string;
  headers: Headers;
};

const defaultOptions: DefaultOptions = {
  baseUrl: '',
  headers: new Headers({
    'Content-Type': 'application/json; charset=UTF-8',
  }),
};

const methods = ['get', 'post', 'put', 'delete', 'patch', 'options'] as const;

export function create(
  options: Partial<DefaultOptions>,
): Record<
  (typeof methods)[number],
  (url: URL | string, options?: RequestInit) => Promise<Response>
> {
  const config = { ...defaultOptions, ...options };

  function getConfig(options: RequestInit = {}, method: string) {
    const optionsHeaders = new Headers(options.headers);
    const configHeaders = new Headers(config.headers);

    const headers = new Headers([...optionsHeaders, ...configHeaders]);

    return {
      ...config,
      ...options,
      headers,
      method: method.toUpperCase(),
    };
  }

  const api = methods.map((method) => {
    return [
      method,
      async (url: URL | string, options: RequestInit) => {
        const { baseUrl, ...init } = getConfig(options, method);
        const requestUrl = `${baseUrl}${url.toString()}`;
        const request = await fetch(requestUrl, init);

        if (!request.ok) {
          throw new Error(request.statusText);
        }

        return request;
      },
    ];
  });

  return Object.fromEntries(api);
}

usage.ts

import { create } from './http';

const http = create({ baseUrl: 'https://jsonplaceholder.typicode.com/' });
const result = await http.get('/posts/1').then((res) => res.json());