idb.js

var db;

function getDB() {
  if (!db) {
    db = new Promise(function(resolve, reject) {
      var openreq = indexedDB.open('keyval-store', 1);

      openreq.onerror = function() {
        reject(openreq.error);
      };

      openreq.onupgradeneeded = function() {
        // First time setup: create an empty object store
        openreq.result.createObjectStore('keyval');
      };

      openreq.onsuccess = function() {
        resolve(openreq.result);
      };
    });
  }
  return db;
}

function withStore(type, callback) {
  return getDB().then(function(db) {
    return new Promise(function(resolve, reject) {
      var transaction = db.transaction('keyval', type);
      transaction.oncomplete = function() {
        resolve();
      };
      transaction.onerror = function() {
        reject(transaction.error);
      };
      callback(transaction.objectStore('keyval'));
    });
  });
}

var idbKeyval = {
  get: function(key) {
    var req;
    return withStore('readonly', function(store) {
      req = store.get(key);
    }).then(function() {
      return req.result;
    });
  },
  set: function(key, value) {
    return withStore('readwrite', function(store) {
      store.put(value, key);
    });
  },
  delete: function(key) {
    return withStore('readwrite', function(store) {
      store.delete(key);
    });
  },
  clear: function() {
    return withStore('readwrite', function(store) {
      store.clear();
    });
  },
  keys: function() {
    var keys = [];
    return withStore('readonly', function(store) {
      // This would be store.getAllKeys(), but it isn't supported by Edge or Safari.
      // And openKeyCursor isn't supported by Safari.
      (store.openKeyCursor || store.openCursor).call(store).onsuccess = function() {
        if (!this.result) return;
        keys.push(this.result.key);
        this.result.continue();
      };
    }).then(function() {
      return keys;
    });
  },
};

export default idbKeyval;