Sends a request to the specified URL.

request.js

/**
 * Sends a request to the specified URL.
 * @param {string} url
 *   The URL to which the request will be sent.
 * @param {?request__Options=} options
 *   The various options to set on the request.
 * @returns {Promise<XMLHttpRequest>}
 *   A promise of the corresponding `XMLHttpRequest`.
 */
function request(url, options) {
  let {data, headers, method, onDone, onSetup, params, type} = options ?? {};
  return new Promise((resolve, reject) => {
    const xhr = new XMLHttpRequest();

    // Capture when the request is done loading...
    xhr.addEventListener("readystatechange", () => {
      if(xhr.readyState === XMLHttpRequest.DONE) {
        const success = 200 <= xhr.status && xhr.status < 400;
        (success ? resolve : reject)(xhr);
        onDone && onDone(
          success,
          xhr.responseXML ?? xhr.responseText ?? xhr.response,
          xhr
        );
      }
    });

    // If params were specified add them to the URL.
    if (params) {
      url = url.replace(
        /\?([^#]*)|(?=#)|$/,
        (_, qs) => {
          const usp = new URLSearchParams(qs);
          for (const [name, values] of Object.entries(params)) {
            for (const value of Array.isArray(values) ? values : [values]) {
              usp.append(name, value);
            }
          }
          return `${usp}` && `?${usp}`;
        }
      );
    }

    // Open the URL using the specified method (defaults to "GET").
    xhr.open(method ?? "GET", url);

    // Set the extra headers if they were specified.
    if (headers) {
      for (const [key, value] of Object.entries(headers)) {
        xhr.setRequestHeader(key, value);
      }
    }
    // Set the content type if specified.
    if (type) {
      // Convert the data for special types:  form-data, form-urlencoded and
      // JSON.
      const [m, isJSON, isFormData] = /^(?:(?:application\/|text\/)?(json)|multipart\/(form-data)|application\/x-www-form-urlencoded)$/i.exec(type) ?? [];
      if (m) {
        if (isJSON) {
          if ('string' === typeof data) {
            try {
              JSON.parse(data);
            }
            catch (e) {
              data = JSON.stringify(data);
            }
          }
          else {
            try {
              data = JSON.stringify(data);
            } catch(e) {}
          }
        }
        else if (data && 'object' === typeof data && !(data instanceof FormData)) {
          const newContainer = isFormData ? new FormData() : new URLSearchParams();
          for (const [key, values] of Object.entries(data)) {
            for (const value of (Array.isArray(values) ? values : [values])) {
              newContainer.append(key, value);
            }
          }
          data = isFormData ? newContainer : newContainer.toString();
          // Remove type if it will be automatically determined via the form
          // data.
          if (isFormData) type = false;
        }
      }
      // Set the type to content-type unless it was removed.
      if (type) xhr.setRequestHeader("Content-Type", type);
    }
    
    // If there is an onSetup() function defined go ahead and call it.
    if (onSetup) onSetup(xhr);

    // Send the request.
    xhr.send(data ?? undefined);
  });
}
/**
 * @typedef request__Options
 * @property {?(FormData|string|Record<string,string|string[]>)=} data
 *   The data sent with the request.
 * @property {?{[key: string]: string}=} headers
 *   The headers to set on the request.
 * @property {?("GET"|"POST"|"PUT"|"PATCH"|"DELETE"|"HEAD"|"OPTIONS")=} method
 *   The method to use to make the request.
 * @property {?((xhr: XMLHttpRequest) => void)=} onSetup
 *   The function that is run right before sending the request.
 * @property {?((success: boolean, response: *, xhr: XMLHttpRequest) => void)=} onDone
 *   The function that is run once the request is done (whether or succeeded
 *   or failed).
   * @property {?Record<string,string|string[]>=} params
   *   The URL parameters to add to any that were already specified in the given
   *   URL.
 * @property {?string=} type
 *   The value of the "Content-Type" header.  This will override the
 *   "Content-Type" header set in `options.headers` unless it is set to
 *   "multipart/form-data" in which case the content-type will be automatically
 *   generated based on the `data` passed in.
 */