Express-interceptor allows you to define a previous step before sending a response. This allows you to do anything you want with the response, such as processing, transforming, replacing, or logging it. Express-interceptor allows you to avoid calling `next()` over and over. Further more, you can avoid managing nested scopes. Using a declarative API, it’s simple to use and maintain.
Some use cases include:
- Transpile custom elements into standard HTML elements.
- Transform JSX or compile less files on the fly.
- Store statistics about responses.
- Set response headers based on tags in the response body.
- Dynamically inject live-reload scripts to HTML.
## Usage
Install the package
npm i --save express-interceptor
Define your interceptor
```javascript
var express = require('express');
var cheerio = require('cheerio');
var interceptor = require('express-interceptor');
var app = express();
var finalParagraphInterceptor = interceptor(function(req, res){
return {
// Only HTML responses will be intercepted
isInterceptable: function(){
return /text\/html/.test(res.get('Content-Type'));
},
// Appends a paragraph at the end of the response body
intercept: function(body, send) {
var $document = cheerio.load(body);
$document('body').append('From interceptor!
'); send($document.html()); } }; }) // Add the interceptor middleware app.use(finalParagraphInterceptor); app.use(express.static(__dirname + '/public/')); app.listen(3000); ``` You're defining an interceptor that will be executed whenever the response contains html as Content-Type. If this is true, it will append a child at the end of the body. In other words, it will transform the response: ```html"Hello world"
``` Into: ```html"Hello world"
From interceptor!
``` See [more examples](https://github.com/axiomzen/express-interceptor/tree/master/examples). Also, you can debug express-interceptor actions using [debug](https://github.com/visionmedia/debug) env variable `DEBUG=express-interceptor`. ## API * `isInterceptable()` (required): is a predicate function where you define a condition whether or not to intercept a response. Returning `true` buffers the request, and proceeds calling `intercept()` as well as `afterSend()`. Typically, you want to check for this condition in the `res` object in the definition of the middleware. * `intercept(body, send)` (required): Parse the body as an encoded string. After processing the body, call `send(newBody)` with the content to be sent back to the client. * `afterSend(oldBody, newBody)`: This method will be called after sending the response to the client – after the `done()` callback in the `send()` method is executed. This method would typically be used to cache something, log stats, fire a job, among other things. ## Who is using it? * [node-stylus-require](https://www.npmjs.com/package/node-stylus-require) * [express-html-minify](https://www.npmjs.com/package/express-html-minify) * [express-jare](https://www.npmjs.com/package/express-jare) * [hospitalrun-server-routes](https://www.npmjs.com/package/hospitalrun-server-routes) ## Similar to - [express-hijackresponse](https://github.com/papandreou/express-hijackresponse) Different API, using callbacks with no top down structure, more obtrusive to HTTP internals. - [hijackresponse](https://github.com/gustavnikolaj/hijackresponse) Attempting to solve same problems than `express-hijackresponse`. Different API using pipes, recommended if you have problems with [streaming](https://github.com/axiomzen/express-interceptor/issues/15) or if you need more control over responses. - [tamper](https://github.com/fgnass/tamper) Similar functionality but different internals and API. ## Words of advice If your `intercept` method make calls to a database, or needs to make expensive transformations to the original response, you should take in account the time that will add to the response. You should define your `isInterceptable` method carefully, checking the type of the response, or even the route that was fired by the request, also you may consider implementing a cache strategy to get faster responses. If you face any issue, don't hesitate to submit it [here](https://github.com/axiomzen/express-interceptor/issues). ## Contributing Please check [CONTRIBUTING.md](CONTRIBUTING.md). This project adheres to the [Open Code of Conduct](http://todogroup.org/opencodeofconduct/#express-interceptor/ipinoraul@gmail.com). By participating, you are expected to honor this code. ## Author * [AxiomZen](https://www.axiomzen.co/). ## Collaborators * [Fabiano Soriani](https://github.com/flockonus). * [Raul Pino](https://github.com/p1nox). ## License [MIT](LICENSE)