compression is a middleware function that compresses the response body that will be send to the client. This module uses the zlib module https://nodejs.org/api/zlib.html that supports the following content-encoding mechanisms:

• gzip
• deflate

The Accept-Encoding HTTP header is used to determine which content-encoding mechanism is supported on the client-side (for example web browser) while the Content-Encoding HTTP header is used to tell the client which content encoding mechanism was applied to the response body.

compression is a configurable middleware function. It accepts an options object as the first argument to define a specific behavior for the middleware and also to pass zlib options as well.