Express (fka Connect) is standard in the sense that the "middleware" API design was/is part of the CommonJs server-side JavaScript (SSJS) initiative [1] from wh

Express (fka Connect) is standard in the sense that the "middleware" API design was/is part of the CommonJs server-side JavaScript (SSJS) initiative [1] from which Node.js originated and insofar as you can write a middleware that plugs into Node.js' core http API and express.js at the same time since these invoke your code using the same basic callback, which was deemed desirable for portability back when Node.js wasn't the only SSJS framework around. Express/connect draws inspiration from Ruby's Sinatra/Rack and Python's WSGI, and is based on JSGI/JackJs. [1]: https://wiki.commonjs.org https://wiki.commonjs.org