Implementing Duplex/Transform Streams

The readable and Writable sides of a duplex stream operate completely independently from one another. A transform stream is the more interesting duplex stream because its output is computed from its input. 

For a transform stream, we don’t have to implement the read or write methods, we only need to implement a transform method, which combines both of them. It has the signature of the write method and we can use it to push data as well. Here’s an example duplex stream which