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Rich Werden

A simple site for Rich to write about code and archive some completed projects for future reference...

#TIL: Express Routing With RegExp

Today, I learned that Express can actually parse inbound/outbound routing paths using Regular Expressions1 for either paths or routing!

When setting up a path for an http request/response, you can actually define the path2 with a handful of regular expressions being used inline… Now, as often happens, this is a RTFM from the official Express docs, but this was news to me (especially because I’m pretty good with RegEx).

For mixing routes you can put some of the regexp search modifiers [?, +, *, ^/$, ()] right into the address string of what would otherwise be .get('a*/norma?l/:path, ....). BUT watch out because dot . and dash- are treated LITERALLY!, not like their normal use in regex

If you want to use pure regexp (and I probably would, but that’s me), you use Javascript’s normal regexp /search/ style, but leave out the quotes from the first term of the handler. Don’t '/doThis/', instead /doThis/, and this way you can use a .get(/d.t/, ...).

There are some great regex tools out there. Personally, I’m partial to for my quick regexp testing. The docs do mention this [Express Route Tester][test] tool for testing routes and showing you the regexp your '/endpoint:someparam' is actually being compiled to, but since it doesn’t support pattern-matching, I’m not sure that it is super useful in this regard.

Code Time…

var express = require('express')
var app = express()

/* Ex1: I want to send the same `foo.html` as the response to */
/* requests coming into `` OR `` */
// In regex `?` means 'optional'
app.get('/A(NT)?(MP)?', (req, res) => {

/* Ex2: I want to respond to requests to `` as */
/* well as to `` but NOT to `` */
// In regex `*` means 'anything' and `$` means 'the end'
app.get('/*down$', (req, res, next) => { /*...*/} )


After years of bopping between environments, one of the few things that remains constant from one to another is the use of the absurd syntax that is Regular Expressions. It is total gobbledygook4 and I know it primarily because I’ve used it in ‘Find’ commands in the multipleplusplus textst editorsvsc that I’ve used over the years. Knowing regex is up there with learning vi or Emacs on the ‘things ya should know’ pile, but I gotta say, it is really useful to know.

  1. I personally call it ‘RegEx’/’regex’, but since javascript is my bread-and-butter at the moment, they use ‘RegExp()’ so #whatcanyado I just use them all interchangably. 

  2. Per the docs - “Query strings are not part of the route path.” - This is not about query strings or things after a ‘?’. Here we’re dealing with the raw inbound URI. 

  3. Yes, the first example would also match ‘/ANTMP’ and the second example matches anything that ends in ‘down’. 

  4. Technical Terminology