metamask-extension/ui/app/helpers/utils/fetch-with-cache.js

import { getStorageItem, setStorageItem } from '../../../lib/storage-helpers';
import getFetchWithTimeout from '../../../../shared/modules/fetch-with-timeout';

const fetchWithCache = async (
  url,
  fetchOptions = {},
  { cacheRefreshTime = 360000, timeout = 30000 } = {},
) => {
  if (
    fetchOptions.body ||
    (fetchOptions.method && fetchOptions.method !== 'GET')
  ) {
    throw new Error('fetchWithCache only supports GET requests');
  }
  if (!(fetchOptions.headers instanceof window.Headers)) {
    fetchOptions.headers = new window.Headers(fetchOptions.headers);
  }
  if (
    fetchOptions.headers.has('Content-Type') &&
    fetchOptions.headers.get('Content-Type') !== 'application/json'
  ) {
    throw new Error('fetchWithCache only supports JSON responses');
  }

  const currentTime = Date.now();
  const cacheKey = `cachedFetch:${url}`;
  const { cachedResponse, cachedTime } = (await getStorageItem(cacheKey)) || {};
  if (cachedResponse && currentTime - cachedTime < cacheRefreshTime) {
    return cachedResponse;
  }
  fetchOptions.headers.set('Content-Type', 'application/json');
  const fetchWithTimeout = getFetchWithTimeout(timeout);
  const response = await fetchWithTimeout(url, {
    referrerPolicy: 'no-referrer-when-downgrade',
    body: null,
    method: 'GET',
    mode: 'cors',
    ...fetchOptions,
  });
  if (!response.ok) {
    throw new Error(
      `Fetch failed with status '${response.status}': '${response.statusText}'`,
    );
  }
  const responseJson = await response.json();
  const cacheEntry = {
    cachedResponse: responseJson,
    cachedTime: currentTime,
  };

  await setStorageItem(cacheKey, cacheEntry);
  return responseJson;
};

export default fetchWithCache;