Abstract: Because of the asynchronous characteristic of I/O，Node.js is quite suitable for developing server-side JavaScript applications. To implement concurrent asynchronous I/O control，developers have to write tedious code manually，it becomes a barrier to developers. Based on the concurrent counter，a concurrent flow- control framework can be constructed. The framework achieved concurrent control between multiple asynchronous I/O in a direct viewing way. Thus，it benefits server- side JavaScript developments and also promotes the efficiency of development.

Key words: asynchronous I/O, concurrency, synchronization, concurrent counter, JavaScript