pspdfkit-indexeddb-cache-sample.js

function getCache(name) {
  return new Promise((resolve, reject) => {
    const version = 1;
    const request = indexedDB.open(name, version);

    request.onsuccess = event => {
      const db = event.target.result;

      /*
       * Returns a Promise that resolves with an object
       * which contains { put, get } helpers.
       */
      resolve({
        put: (key, value) =>
          new Promise((resolve, reject) => {
            try {
              const result = db
                .transaction([name], "readwrite")
                .objectStore(name)
                .put(value, key);

              result.onsuccess = resolve;
              result.onerror = reject;
            } catch (e) {
              reject(e);
            }
          }),

        /*
         * Returns a Promise that resolves with the `value` for `key`.
         */
        get: key =>
          new Promise((resolve, reject) => {
            try {
              const result = db
                .transaction([name])
                .objectStore(name)
                .get(key);

              result.onsuccess = event => {
                resolve(event.target.result);
              };
              result.onerror = reject;
            } catch (e) {
              reject(e);
            }
          })
      });
    };

    // This will open/create the database.
    request.onupgradeneeded = event => {
      const db = event.target.result;
      db.createObjectStore(name);
    };

    request.onerror = reject;
  });
}