An example of using POST method in a Saga.

saga_post_method.js

function statusHelper(response) {
  if (response.status >= 200 && response.status < 300) {
    return Promise.resolve(response);
  }
  return Promise.reject(new Error(response.statusText));
}

/* Function: handle the async api call
 * Params:
 *   url: api url
 *   method: GET/POST...
 *   body: an javascript object, for POST method only
 * Return:
 *   a Promise, which should be passed to a saga yield call function
 *   if server return success, resolve { res: ...returned result }
 *   if server return failure, resolve { err: ...error message }
 */
function fetchUrl(url, body) {
  // url is only the last part of the full path
  return fetch(`/api${url}`, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Accept: 'application/json',
    },
    body: JSON.stringify(body),
  })
  .then(statusHelper)
  .then(response => response.json())
  .then(res => ({ res }))
  .catch(err => ({ err }));
}

/* Function: an example of using post method in saga
 */
function* userRequestsModuleCodeSaga(action) {
  const moduleName = action.payload.moduleFqn;
  const { res, err } = yield fetchUrl('/module/module_code', { moduleName });
  yield put(moduleActions.serverReturnedCurrentModuleCodeEvt({ res, err }));
}