Modifying Express.js Request Object

Question

In express.js, I would like to provide an additional attribute on the request object for each of my URI listeners. This would provide the protocol, hostname, and port number. For example:

app.get('/users/:id', function(req, res) {
  console.log(req.root); // https://12.34.56.78:1324/
});

I could of course concatenate req.protocol, req.host, and somehow pass around the port number (seems to be missing from the req object) for each one of my URI listeners, but I'd like to be able to do it in a way that all of them could access this information.

Also, the hostname can vary between request (the machine has multiple interfaces) so I can't just concatenate this string when the application launches.

The goal is to provide URI's to the consumer which point to further resources in this API.

Is there some sort of way to tell Express that I want req objects to have this additional information? Is there a better way to do this than what I'm outlining?

Jonathan Lonowski · Accepted Answer · 2012-09-20 18:13:49Z

79

You can add a custom middleware that sets the property for each request:

app.use(function (req, res, next) {
    req.root = req.protocol + '://' + req.get('host') + '/';
    next();
});

Using req.get to obtain the Host header, which should include the port if it was needed.

Just be sure to add it before:

app.use(app.router);

answered Sep 20, 2012 at 18:13

Jonathan Lonowski

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2 Comments

Sebastian Gabriel Vinci Over a year ago

@AdamPietrasiak it is not constant, if you have more than one domain (for example 'your-app.com', 'your-app.com.ar' and 'your-app.com.br'), it will be necessary to check the domain for each request.

Thecave3 Over a year ago

app.router is deprecated btw

hexacyanide · Accepted Answer · 2014-10-19 21:23:13Z

37

You can extend the express.request prototype.

edited Oct 19, 2014 at 21:23

hexacyanide

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answered Sep 23, 2012 at 23:11

TJ Holowaychuk

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3 Comments

redben Over a year ago

like require("express").request.prototype.foo = function(){} ?

neiker Over a year ago

Extend express.request just don't apply in this case, unless for some reason https on his root property never change, otherwise you need to use a middleware and get req.protocol... Anyway, if you want to extend request (and thats actually why I found this question) just use express.request.getFooParam = function () { return this.param('foo'); }

Nelo Mitranim Over a year ago

Exactly what I was looking for. Logged in to give a thumbs up, no need for middleware when you can go to the root and extend the prototype.

DeadAlready · Accepted Answer · 2012-09-20 18:12:50Z

9

The best way to modify the request object is to add your own middleware function before the app.router declaration.

    app.use(function(req, res, next){
      // Edit request object here
      req.root = 'Whatever I want';
      next();
    });
    app.use(app.router);

This will modify the request object and every route will be able to access req.root property, so

    app.get('/',function(req, res, next){
      console.log(req.root); // will print "Whatever I want";
    });

answered Sep 20, 2012 at 18:12

DeadAlready

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Comments

Mattias · Accepted Answer · 2012-09-20 18:13:12Z

4

You can use a middleware. Add this to your app.configure block:

app.use(function (req, res, next) {
  req.root = 'WHAT YOU WANT';
  next();
});

Every request will go tough this function, and afterwards go to the right url-block thanks to next().

answered Sep 20, 2012 at 18:13

Mattias

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Comments

apflieger · Accepted Answer · 2022-03-15 16:06:46Z

1

Express was designed to support this in the response object, not the request. The response object support custom variables in res.locals. See http://expressjs.com/en/4x/api.html#res.locals

This is particularly useful for typescript users. The locals property is typed Record<string, any>

edited Mar 15, 2022 at 16:06

answered Oct 19, 2020 at 9:38

apflieger

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3 Comments

olegario Over a year ago

This has nothing to do with the question. We are looking for ways to modify request object.

OneCricketeer Over a year ago

res.locals says it is for template rendering... PassportJS, for example, updates the request to add a user field, so this is definitely not correct.

Martin Bories Over a year ago

While not intended for this use-case, this is a better solution for me as a TypeScript user (manipulating the req-object in the way suggested in the other answers is not better).

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