How to detect whether a request will be handled by a route later in the stack?

[markcellus]

Sorry if this has already been addressed, but couldn't find anything in searching. What is the best way to know whether the URL in a request has a request handler associated before that handler is executed? In other words, given the express server below:

const app = express();
app.use((req, res) => {
   // check if req matches any routes below it in this file
});

app.get('/abc', (req, res) => {
   // do some stuff
});
app.get('/xyz', (req, res) => {
  // do some stuff
});

How can my first use handler detect whether the request will match any of the routes below it, even if they were to change in the future?

[ViniciusMarchi]

Hi. I don't know if there are better ways to do this, but here's one that might help you. You can iterate over app._router.stack property. This property stores a list of all routes registered in your app. Here is a example:

const express = require('express')
const app = express();

app.use((req, res, next) => {
  let hasRouteToHandle = false;
  app._router.stack.forEach((stackItem) => {
    // check if current rout path matches route request path
    if (stackItem.route?.path === req.path) {
      hasRouteToHandle = true;
    }
  });


  if (hasRouteToHandle) {
    console.log('Request will be handled by a route later in the stack')
  } else {
    // No matching route for this request
    console.log('Request will not be handled')
  }

  
  next(); // to continue to next route
});


app.get('/abc', (req, res) => {
   // do some stuff
});
app.get('/xyz', (req, res) => {
  // do some stuff
});

app.listen(3000)

[markcellus]

Ah yes, thanks. Iterating over the stack works. I like that the stacks also have the regex so I can do matching based off of that as well.

It does seem like these stacks are a private API, however. Can I really rely on them? And are they subjected to change in the future?

[ViniciusMarchi]

Yes you are correct, because of this I mentioned not knowing if there is a better way to implement this. Accessing private attributes may not be the best option. But luckily I researched and found a better option using the Router.

Look at the previous example refactored to use this option

const express = require('express')
const app = express();
const router = express.Router(); // use router

router.use((req, res, next) => {
  let hasRouteToHandle = false;
  router.stack.forEach((stackItem) => {
    // check if current rout path matches route request path
    if (stackItem.route?.path === req.path) {
      hasRouteToHandle = true;
    }
  });


  if (hasRouteToHandle) {
    console.log('Request will be handled by a route later in the stack')
  } else {
    // No matching route for this request
    console.log('Request will not be handled')
  }

  
  next(); // to continue to next route
});

router.get('/abc', (req, res) => {
   // do some stuff
});
router.get('/xyz', (req, res) => {
  // do some stuff
});

app.use(router);

app.listen(3000)

Using Router the attribute that accesses the stack is not private and the Router is already prepared to store and provide information about the routes.

[markcellus]

Great, I'll use the direct router instance for the stacks like you've shown above. Thanks again!