DBMagic with Promises

class DBMagic {
  constructor( db_name, db_version, stores ) {
    if ( typeof stores === 'string' ) stores = [ stores ];

    this.stores = stores;
    this.db_name = db_name;
    this.db_version = db_version;
    var indexedDB = window.indexedDB || window.mozIndexedDB || window.webkitIndexedDB || window.msIndexedDB;
    this.indexedDB = indexedDB;

    this.db_delete();
    this.db_create();
    this.tables = {};
  }

  store( name, mode ) {
    return new Promise( ( resolve, reject ) => {
      const req = this.indexedDB.open( this.db_name, this.db_version );
      req.onerror = ( e ) => { reject( e ); };
      req.onsuccess = () => {    let db = req.result;
        if (! db.objectStoreNames.contains( name ) ) {
         reject( 'Store [' + name + '] Not Found.'  );
        } else {
          let tx = db.transaction ( [ name ], mode );
          resolve( tx.objectStore( name ) );
        }
      };
    } );
  }

  add( name, items ) {
    if ( ! Array.isArray( items ) ) items = [ items ];

    return new Promise( ( resolve, reject ) => {
      this.store( name, 'readwrite' ).then( store => {
        items.forEach( item => {
          const req = store.add( item );
          req.onerror = () => {
            resolve( item.id );
          };
          req.onsuccess = ( e ) => {
            if ( debug )
              log( 'SUCCESS: Added key ['+ item.id +'] to store [' +
              name + '] on database [' + this.db_name + ']' );
            resolve( item.id );
          };
        } );
      } );
    } );
  }

  get( name, items ) {
    if ( typeof items === 'string' ) items = [ items ];

    return new Promise( ( resolve, reject ) => {
      this.store( name, 'readonly' ).then( store => {
        items.forEach( item => {
          const req = store.get( item );
          req.onerror = ( e ) => {
            if ( debug )
              log( 'ERROR: [get] Could not retrieve key from store [' + name +
              ' on database' + this.db_name + ']\n', e.srcElement.error );
            reject( e );
          };
          req.onsuccess = () => {
            if ( debug )
              log( 'SUCCESS: Retrieved key ['+ item +'] from store [' +
              name + '] on database ['+ this.db_name +']' );
            resolve( req.result );
          };
        } );
      } );
    } );
  }

  getAll( name ) {
    return new Promise( ( resolve, reject ) => {
      this.store( name, 'readonly' ).then( store => {
        const req = store.getAll();
        req.onerror = ( e ) => {
          if ( debug )
            log( 'ERROR: [getAll] Could not retrieve keys from store [' +
            name + ' on database' + this.db_name +']\n', e.srcElement.error );
          reject( e );
        };
        req.onsuccess = () => {
          if ( debug )
            log( 'SUCCESS: Retrieved all keys from store [' + name +
            '] on database ['+ this.db_name +']' );
          resolve( req.result );
        };
      } );
    } );
  }

  update( name, items ) {
    if ( ! Array.isArray( items ) ) items = [ items ];

    return new Promise( ( resolve, reject ) => {
      this.store( name, 'readwrite' ).then( store => {
        items.forEach( item => {
          const req = store.put( item );
          req.onerror = ( e ) => {
            if ( debug )
              log( 'ERROR: Updating key [' + item.id + '] in store [' +
              name + '] on database [' + this.db_name + ']\n',
              e.srcElement.error );
            reject( e );
          };
          req.onsuccess = ( e ) => {
            if ( debug )
              log( 'SUCCESS: Updated key ['+ item.id +'] in store [' +
              name + '] on database [' + this.db_name + ']' );
            resolve( e );
          };
        });
      } );
    } );
  }

  delete( name, items ) {
    if ( typeof items === 'string' ) items = [ items ];

    return new Promise( ( resolve, reject ) => {
      this.store( name, 'readwrite' ).then( store => {
        items.forEach( item => {
          const req = store.delete( item );
          req.onerror = ( e ) => {
            if ( debug )
              log( 'ERROR: Deleted key [' + item + '] from store [' +
              name + ']\n', e.srcElement.error );
            reject( e );
          };
          req.onsuccess = ( e ) => {
            if ( debug )
              log( 'SUCCESS: Deleted key [' + item + '] from store [' +
              name + '] on database [' + this.db_name + ']' );
            resolve( e );
          };
        } );
      } );
    } );
  }

  deleteAll( name ) {
    return new Promise( ( resolve, reject ) => {
      this.store( name, 'readwrite' ).then( store => {
        const req = store.clear();
        req.onerror = ( e ) => {
          if ( debug )
            log( 'ERROR: Could not delete keys from store [' + name +
            '] on database [' + this.db_name + ']\n', e.srcElement.error );
          reject( e );
        };
        req.onsuccess = ( e ) => {
          if ( debug )
            log( 'SUCCESS: Deleted all keys from store [' +
            name + '] on database [' + this.db_name + ']' );
          resolve( e );
        };
      });
    } );
  }

  db_create() {
    const req = this.indexedDB.open( this.db_name, this.db_version );

    return new Promise( (resolve, reject) => {
      req.onerror = () => {
        let db = req.result;
        if ( debug )
          log( 'ERROR: Database [' + this.db_name +
          '] could not be opened successfully, [ version = ' + db.version + ' ]' );
        reject( true );
      };

      req.onsuccess = () => {
        let db = req.result;
        if ( debug )
          log( 'SUCCESS: Database [' + this.db_name +
          '] opened successfully, [ version = ' + db.version + ' ]' );
        resolve( true );
      };

      req.onupgradeneeded = ( e ) => {
        let db = req.result;

        switch( e.oldVersion ) {
          case 0:
            this.stores.forEach( name => {
              db.createObjectStore( name, { keyPath: 'id' } );
            } );
          case 1:
            let oldVersion = e.oldVersion;
            let newVersion = e.newVersion;
            if ( debug ) log( db.objectStoreNames );
        }
      };
    } );
  }

  db_delete() {
    const db_name = this.db_name;
    this.indexedDB.deleteDatabase( db_name );

    return new Promise( (resolve, reject) => {
      if ( debug )
        log('SUCCESS: Database ['+ db_name +'] deleted successfully.');
      resolve( true );
    } );
  }
}