在同一个“会话”中可以打开多个连接（一个接一个地关闭等）（会话是什么意思？）。
例如：

function open(name) {
  return new Promise((resolve, reject) => {
    const request = indexedDB.open(name);
    request.onsuccess = event => resolve(request.result);
    request.onerror = event => reject(request.error);
  });
}

async function main() {
  for (let i = 0; i < 10; i++) {
    console.log('Opening database connection', i);
    const connection = await open('mydb');
    console.log('Database connection %s opened to', i, connection.name);

    // do stuff with the connection here

    console.log('Requesting database connection %s to close eventually', i);
    connection.close();
  }
}

main().catch(console.error);