Connect or Express middleware to modify the response.body

I would like to have a middleware function which modifies the response body.

This is for an express server.

Something like:

function modify(req, res, next){
  res.on('send', function(){
    res.body = res.body + "modified"



I don't understand what event to listen for. Any help or documentation would be appreciate.

You don't need to listen to any events. Just make it

function modify(req, res, next){
  res.body = res.body + "modified";


And use it after you use the router. This way after all your routes have executed you can modify the body

Modify response in express.js or any connect application (Example), A protip by avgp about nodejs, express.js, martin-n, and connect.js. /9896628/ connect-or-express-middleware-to-modify-the-response-body� Intercept response body or transform response body in express which, ever way you call it, one thing is for sure its not as straight forward as it is for the request body object. In this tutorial we will write an express middleware to intercept the response body object of an API request .

I believe the OP actually wants to modify the response stream once a middleware has handled the request. Look at the bundled Compress middleware implementation for an example of how this is done. Connect monkey patches the ServerResponse prototype to emit the header event when writeHead is called, but before it is completed.

Connect or Express middleware to modify the response.body, I would like to have a middleware function which modifies the response body. This is for an express server. Something like: function modify(req, res, next){� @hallas Thanks for the help - the reason for the crazy middleware is grunts auto-reload task (needs to inject some js into the page when running) @jonathanong Interesting, If I hook res.write instead of send it never fires, admittedly I am using another layer on top of express (locomotive) but I couldnt see any reason why.

express-mung is designed for this. Instead of events its just more middleware. Your example would look something like

const mung = require('express-mung')

module.exports = mung.json(body => body.modifiedBy = 'me');

Middleware that needs to modify res.body � Issue #1583 � expressjs , If I send the raw body instead of the res object, it will crap out because req is lost, with it like this the http response never returns though express� i currently have a running server using nodejs, mongo, express and W2UI for the front end. W2ui requests come in an a record array that has all the parameters record[name]:foo i want to write a middleware that edits requests and changes them before they reach the route.

Overwriting the response's write method seemed to work for me with Express 4. This allows modifying the response's body even when it's a stream.

app.use(function (req, res, next) {
  var write = res.write;
  res.write = function (chunk) {
    if (~res.getHeader('Content-Type').indexOf('text/html')) {
      chunk instanceof Buffer && (chunk = chunk.toString());
      chunk = chunk.replace(/(<\/body>)/, "<script>alert('hi')</script>\n\n$1");
      res.setHeader('Content-Length', chunk.length);
    write.apply(this, arguments);

Just make sure to register this middleware before any other middleware that may be modifying the response.

Express middleware, See also: body, co-body, and raw-body. express.bodyParser. compression, Compress HTTP responses. express.compress. connect-rid, Generate unique request� GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. An express middleware to log response body, intercept response body or to modify response body, in an NodeJS express app. Use Git or checkout with SVN using the web URL.

There seems to be a module for doing just this called connect-static-transform, check it out:

A connect middleware which allows transformation of static files before serving them.

And it comes with examples, like this one.

Express body-parser middleware, Parse incoming request bodies in a middleware before your handlers, available the suggested HTTP response code, an expose property to determine if the message Express/Connect top-level generic All the parsers accept a type option which allows you to change the Content-Type that the middleware will parse. But just throw in connect.static (a middleware that comes with Connect), configured to point to a directory, and your server will provide access to the files in that directory. Note that Express provides Connect's middlewares also; express.static is the same as connect.static. (Both were known as staticProvider until recently.)

Intercept response body in NodeJS express app — CipherTrick, An express middleware to log response body, intercept response body or to modify response body, in an NodeJS express app. Express/Connect top-level generic. This example demonstrates adding a generic JSON and URL-encoded parser as a top-level middleware, which will parse the bodies of all incoming requests. This is the simplest setup.

Build and Understand Express Middleware through Examples, Express middleware are functions that execute during the lifecycle of a request to Each middleware has access to the HTTP request and response for each Okta is a cloud service that allows developers to create, edit, and securely options so that Okta knows how to connect to your Okta application. Note: the issue referenced in this post has been fixed and will get released with ASP.NET Core 1.1.0. While creating a small piece of middleware to modify the response body's content, I had trouble getting anything to appear in my browser.

Koa, Koa is a new web framework designed by the team behind Express, which aims to you may have encountered such as Ruby's Rack, Connect, and so on - however a response app.use(async ctx => { ctx.body = 'Hello World'; }); app. listen(3000); You can only edit these properties (not recommended) by using Object. This middleware is available in Express v4.17.0 onwards. This is a built-in middleware function in Express. It parses incoming request payloads into a Buffer and is based on body-parser. Returns middleware that parses all bodies as a Buffer and only looks at requests where the Content-Type header matches the type option.