Where Promises.js came in?

Those of you who are aware of how a server-side script executes in an I/O event know that reading or writing data to and from a drive is blocking in nature, that is, during its execution, no other operation can be performed by a server-side language, even by the client. Well, with Promises.js, this is no longer the case. Promises.js utilizes a nonblocking strategy to perform I/O operations, so a client using your web app is free to perform any other tasks they want to without having to wait for the data read/write operation to be completed.