Express Middleware

Reading Materials

• Using Express Middleware
• Middleware on TutorialsPoint
• JsWiz Video on Express Middleware

JsWiz Video

Surprisingly, we've been using express middleware all along, with the app.uses() call, we just didn't know what it meant. Now, armed with a better understanding of chaining events, this makes total sense! The diagram shown in the video by JsWiz is a great visual about how and where middleware takes effect:

It's also nice to know there is an alternate way to instantiate middleware. The app.uses('middleware') call instantiates middleware for all routes defined after the line number of the app.uses() call. A different method instantiates the middleware only to selected routes. The way to do this is: app.METHOD('route-name', 'middleware', 'middleware', 'final handler')

Using Express Middleware

Middleware comes in 5 forms:

• Application-level: middleware that you define and apply with app.use() so that it takes effect for all methods
• Router-level: middleware that you define and apply with route.use() so that it takes effect for one router
• Error-handling: middleware that deals with error conditions
• Built-in: the following 3 functions are built-in: express.static, express.json, express.urlencoded
• Third-party: needs to be installed and required as a Node.js module. Then it can be loaded at the application or router level.

Middleware on TutorialPoint

A listing of commonly used third-party middleware:

• body-parser
• cookie-parser
• express-session