DBMagic with update method.

const log = console.log;

class Table {
  constructor( db, name, debug=false) {
    this.db = db;
    this.dbName = db.db;
    this.store = name;
    this.debug = debug;

    this.indexedDB = window.indexedDB || window.mozIndexedDB ||
    window.webkitIndexedDB || window.msIndexedDB;

    return this.table( name );
  }

  table( store ) {
    let stores = this.db.stores;

    const do_upgrade = () => {
      stores.push( store );

      return new Promise( ( resolve, reject ) => {

        let req = this.indexedDB.open( this.dbName, stores.length + 1 );

        req.onerror = e => reject( e );
        req.onsuccess = () => {
          this.db.stores.push( store );
          req.result.close();
          resolve( this );
        };
        req.onupgradeneeded = () => req.result
        .createObjectStore( store, { keyPath: 'id' } );
      } );
    };

    return new Promise( ( resolve, reject ) => {
     let openReq = this.indexedDB.open( this.dbName );

      openReq.onerror = () => {
        do_upgrade();
        resolve( this );
      };

      openReq.onsuccess = () => {
        openReq.result.close();
        if ( ! stores.includes( store ) ) {
          do_upgrade();
        }
        resolve( this );
      };
    } );
  }

  add_que( args ) {
    return new Promise(( resolve, reject ) => {
      let openReq = this.indexedDB.open( this.dbName );

      openReq.onerror = e => reject( e );

      openReq.onsuccess = () => {
        let tx = openReq.result.transaction ( [ this.store ], 'readwrite' );
        let addReq = tx.objectStore( this.store ).add( args );
        tx.commit();

        addReq.onerror = e => {
          if ( this.debug )
            log( `[ ERROR:add ], could not add key [${ args.id }] in store [${
            addReq.source.name }] in database [${ this.dbName }]` );
          reject( e );
        };

        addReq.onsuccess = () => {
          if ( this.debug )
            log( `[ INFO:add ], Added key [${ args.id }] in store [${
            addReq.source.name }] in database [${ this.dbName }]` );
          resolve( this );
          openReq.result.close();
        };
      };
    } );
  }

  async add( args ) {
    if ( ! Array.isArray( args ) ) args = [ args ];
    let promises = [];
    args.forEach( item => { promises.push( this.add_que( item ) ); } );
    await promises;
    return this;
  }

  update( args ) {
    return this.get( { id: args.id } ).then( values => {
      args = Object.assign({}, values, args );

      return new Promise(( resolve, reject ) => {
        let openReq = this.indexedDB.open( this.dbName );

        openReq.onerror = e => reject( e );

        openReq.onsuccess = () => {
          let tx = openReq.result.transaction ( [ this.store ], 'readwrite' );
          let addReq = tx.objectStore( this.store ).put( args );
          tx.commit();

          addReq.onerror = e => {
            if ( this.debug )
              log( `[ ERROR:add ], could not update key [${ args.id }] in store [${
              addReq.source.name }] in database [${ this.dbName }]` );
            reject( e );
          };

          addReq.onsuccess = () => {
            if ( this.debug )
              log( `[ INFO:update ], Updated key [${ args.id }] in store [${
              addReq.source.name }] in database [${ this.dbName }]` );
            resolve( this );
            openReq.result.close();
          };
        };
      } );
    } );
  }

  get( args ) {
    let store = this.store;
    let dbName = this.dbName;

    return new Promise( ( resolve, reject ) => {
      var openReq = this.indexedDB.open( dbName );

        openReq.onerror = e => reject( e );

        openReq.onsuccess = () => {
          let tx = openReq.result.transaction ( [ store ], 'readonly' );

          let obj = tx.objectStore( store );
          let req = args ? obj.get( args.id ) : obj.getAll();
          req.onerror = e => {
            if ( this.debug )
              log( `[ ERROR:getAll ], could not retrieve keys from store [${
              req.source.name }] in database [${ dbName }]` );
            reject( e );
          };

          req.onsuccess = () => {
            if ( this.debug )
              log( `[ INFO:getAll ], Retrieved all keys from store [${
              req.source.name }] in database [${ dbName }]` );
            resolve( req.result );
            openReq.result.close();
          };
        };
    } );
  }

}

class DB {
  constructor( name, debug=false) {
    this.db = name;
    this.debug = debug;
    this.stores = [];
    this.upgrade = false;
    this.init();
  }

  init() {
    let indexedDB = window.indexedDB || window.mozIndexedDB ||
    window.webkitIndexedDB || window.msIndexedDB;

    return new Promise( ( resolve, reject ) => {
      let req = indexedDB.open( this.db );

      req.onerror = e => reject( e );
      req.onsuccess = () => { req.result.close(); resolve(); };
      req.onupgradeneeded = () => { return true; };
    } );
  }

  table( name ) {
    let tbl = new Table( this, name, this.debug );

    return tbl;
  }
}



jQuery( document ).ready( () => {
  $( '#testDB' ).on( 'click', function() {

    $( 'body' ).append( $( '<div></br>Creating the databases.</div>' ) );
    let db1 = new DB( 'MyDB1', true );
    const setup = async () => {
        let tbl = await db1.table( 'users' );
        await tbl.add( { id: 1, fName: 'Joe', lName: 'Doe', group: 3 } );
        await tbl.add( [
        { id: 2, fName: 'Jane', lName: 'Doe', group: 1 },
        { id: 3, fName: 'Peter', lName: 'Parker', group: 2 }
        ] );

        log('Test 1 Read data:', await tbl.get() );
        await tbl.update( { id: 2, fName: 'Mary', lName: 'Smith', group: 3 } );
        log('Test 1 Updated data:', await tbl.get() );

    };
    setup();

    let db2 = new DB( 'MyDB2', true );
    db2.table( 'users' )
    .then( tbl => {
        return tbl.add( [
        { id:1, fName: 'Joe', lName: 'Smith', group: 2 },
        { id:2, fName: 'Jane', lName: 'Smith', group: 3 }
        ] );
    } )
    .then( tbl => { return tbl.get(); } )

    .then( results => {
        log('Results:', results );
            $( 'body' ).append( $( '<div></br>Databases created, check the console now.</div>' ) );
        } );
    } );
} );