Middlewares#

Middlewares are functions that process the request, chained one by one, which make them very easy to re-use. Using middlewares you can handle authentication, logging, permissions, etc.

A middleware has access to the req and the res objects from the Node http module. If using afterCtxMiddlewares, you also get access to the route RequestContext.

Learn more about them from Koa's documentation or from Express's documentation

Usage#

You can add middlewares to an EntityRouter by passing them in the EntityRouteOptions, which means that you can both register a local middleware for a specific EntityRouter or register global middlewares by passing them to the makeEntityRouters.

The implementation itself of a middleware will depend of the maker used.

If you use Koa, you can use the makeKoaEntityRoutersmaker.
If you use Express or a compatible API (Next, Nuxt, etc.), you can use the makeExpressEntityRouters maker.

A basic middleware looks like this :

#typescript
1const logMw = async (ctx, next) => {
2    const start = Date.now();
3    await next();
4    const ms = Date.now() - start;
5    ctx.set("X-Response-Time", `${ms}ms`);
6};
Example taken from https://koajs.com/

#typescript
1const timeMw = function (req, res, next) {
2    console.log("Time:", Date.now());
3    next();
4};
Example taken from https://expressjs.com/fr/guide/using-middleware.html

Differences with hooks#

If you want to intervene at some point of the request handling (and potentially alter part), you might want to check hooks rather than using middlewares.

They differ from middlewares since they do not receive the context/req/res arguments but rather just the relevant parts of what they are dedicated to.

Middlewares are more powerful, they can for example end the request handling and send a response, whereas hooks can at most alter their part.

Request Context

Hooks