Express.js internal, where are stored the mount paths on the app object?

Question

I'm facing a very specific use case, where I need to access the mount paths of various express sub apps when iterating over the app object.

Sample code :

const express = require("express")
const app = express()

app.use("/users", new usersRouter())
app.use("/flowers", new flowersRouter())

// Later in code...
app.get("/something", (req, res, next) => checkAppObject(app, next))

function checkAppObject(app, next) {
    // Where are stored the "/users" and "/flowers" info ?
    console.log(app) 
    next()
}

I didn't find it anywhere

Answer 1

As it turns out, the express app object contains an internal _router.stack property which is populated by a collection of Layer objects.

When doing app.use('/path', someFunc), express adds a Layer object and if this someFun is also a router (an app object itself), then the layer.handle object will also contain its own stack property (and so on recursively).

Hence, the only way to access the mount point is on this layer object, inside a regexp. One would have to serialize a regex or something (if that's even possible, see this)

Provided the mount path is "/batchs" the value on the layer object is :

{ /^\/batchs\/?(?=\/|$)/i fast_star: false, fast_slash: false }

on my computer.

Hope this helps