fetcher.js

export function Fetcher (options) {
  if (options.base) this.base = options.base;
};

Fetcher.prototype.fetch = function(input, init) {
  if (input instanceof Request) {
    return window.fetch(input, init);
  }

  let url = this.base ? new URL(input, this.base) : new URL(input);

  if (! init) init = {};

  if (! init.headers) {
    init.headers = new Headers();
  } else if ( !( init.headers instanceof Headers) ) {
    init.headers = new Headers(init.headers);
  }

  let is_get = ! init.method || init.method == 'GET' || init.method == 'HEAD';

  // shortcut for query or form data
  if (init.form) {
    let form;
    if (is_get) {
      form = url.searchParams;
    } else {
      if (init.body) {
        return Promise.reject(new Error('The form shortcut should not be used when a body is specified'));
      }

      form = new FormData();
      init.body = form;

      if (! init.headers.has('Content-Type')) {
        init.headers.set('Content-Type', 'application/x-www-form-urlencoded');
      }
    }

    // if not iterable, try to make it iterable with Object.entries
    let items = typeof init.form[Symbol.iterator] === 'function' ? init.form : Object.entries(init.form);
    items.forEach(([key, value]) => form.append(key, value));

    delete init.form;

  // shortcut for JSON
  } else if (init.json) {
    if (init.body) {
      return Promise.reject(new Error('The json shortcut should not be used when a body is specified'));
    }

    init.body = JSON.stringify(init.json);
    delete init.json;

    if (! init.headers.has('Content-Type')) {
      init.headers.set('Content-Type', 'application/json');
    }
  }

  return window.fetch(url.toString(), init);
};

export let fetcher = (new Fetcher()).fetch;