express-interceptor
Advanced tools
A tiny Express response interceptor
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:
Install the package
npm i --save express-interceptor
Define your interceptor
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);
$document('body').append('<p>From interceptor!</p>');
send($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>
<head></head>
<body>
<p>"Hello world"</p>
</body>
</html>
Into:
<html>
<head></head>
<body>
<p>"Hello world"</p>
<p>From interceptor!</p>
</body>
</html>
See more examples.
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.
express-hijackresponse Different API, using callbacks with no top down structure, more obtrusive to HTTP internals.
tamper Similar functionality but different internals and API.
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.
FAQs
A tiny interceptor for Express responses
The npm package express-interceptor receives a total of 38,106 weekly downloads. As such, express-interceptor popularity was classified as popular.
We found that express-interceptor demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 2 open source maintainers collaborating on the project.
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