Function fetchPolyfill

src/polyfills/fetch.js:37–86

(input, init = {})

 * @return {!Promise<!FetchResponse>}
 */
export function fetchPolyfill(input, init = {}) {
  return new Promise(function (resolve, reject) {
    const requestMethod = normalizeMethod(init.method || 'GET');
    const xhr = createXhrRequest(requestMethod, input);

    if (init.credentials == 'include') {
      xhr.withCredentials = true;
    }

    if (init.responseType === 'document' || init.responseType === 'text') {
      xhr.responseType = init.responseType;
    }

    if (init.headers) {
      Object.keys(init.headers).forEach(function (header) {
        xhr.setRequestHeader(header, init.headers[header]);
      });
    }

    xhr.onreadystatechange = () => {
      if (xhr.readyState < /* STATUS_RECEIVED */ 2) {
        return;
      }
      if (xhr.status < 100 || xhr.status > 599) {
        xhr.onreadystatechange = null;
        reject(user().createExpectedError(`Unknown HTTP status ${xhr.status}`));
        return;
      }

      // TODO(dvoytenko): This is currently simplified: we will wait for the
      // whole document loading to complete. This is fine for the use cases
      // we have now, but may need to be reimplemented later.
      if (xhr.readyState == /* COMPLETE */ 4) {
        resolve(new FetchResponse(xhr));
      }
    };
    xhr.onerror = () => {
      reject(user().createExpectedError('Network failure'));
    };
    xhr.onabort = () => {
      reject(user().createExpectedError('Request aborted'));
    };

    if (requestMethod == 'POST') {
      xhr.send(init.body);
    } else {
      xhr.send();
    }
  });
}

/**
 * @param {string} method