Cache Control for Dynamic Data Express.JS

Question

How it is possible to set up a cache-control policy in express.js on JSON response?

My JSON response doesn't change at all, so I want to cache it aggressively.

I found how to do caching on static files but can't find how to make it on dynamic data.

score 80 · Accepted Answer · edited Jul 31 '18 at 14:52

80

The inelegant way is to simply add a call to res.set() prior to any JSON output. There, you can specify to set the cache control header and it will cache accordingly.

res.set('Cache-Control', 'public, max-age=31557600'); // one year

Another approach is to simply set a res property to your JSON response in a route then use fallback middleware (prior to the error handling) to render and send the JSON.

app.get('/something.json', function (req, res, next) {
  res.JSONResponse = { 'hello': 'world' };
  next(); // important! 
});

// ...

// Before your error handling middleware:

app.use(function (req, res, next) {
  if (! ('JSONResponse' in res) ) {
    return next();
  }

  res.set('Cache-Control', 'public, max-age=31557600');
  res.json(res.JSONResponse);
})

Edit: Changed from res.setHeader to res.set for Express v4

edited Jul 31 '18 at 14:52

answered Aug 23 '14 at 17:40

Jason

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isn't it `res.header('Cache-Control', 'public, max-age=31557600')` ? – Yuri Astrakhan May 12 '15 at 15:13
11

Be carefull, in Express 4.x, you have to use `res.set({ headers })` or `res.header({ headers })` instead of `res.setHeader({ headers })` as [it is now documented](http://expressjs.com/api.html#res.set). – Clément Fiorio Jun 11 '15 at 10:25
don't forget about `immutable` http://bitsup.blogspot.com/2016/05/cache-control-immutable.html – pravdomil Apr 19 '18 at 15:48
This didn't worked for me. I had posted similar question and still awaiting an answer. Can anyone help me with this ? Question link: https://stackoverflow.com/questions/55700579/setting-cache-control-pubic-not-caching-xhr – VISHAL DAGA Apr 24 '19 at 10:49
1

what does the `public` in the header do? – João Pimentel Ferreira Jun 01 '20 at 23:46
The public response directive indicates that a resource can be cached by any cache. It's not client specific. – 0x1gene Dec 18 '20 at 21:40
How to delete the public cache, using api response. I tried cache-control: no-cache, no-store but not working. – Himanshu Shekhar Sep 22 '21 at 11:53

score 7 · Answer 2 · edited Jun 24 '19 at 09:55

7

You can do it like this, for example :

res.set('Cache-Control', 'public, max-age=31557600, s-maxage=31557600'); // 1 year

edited Jun 24 '19 at 09:55

akmozo

9,829
3
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answered Mar 09 '18 at 12:53

Bằng Nguyễn Hữu

89
1
1

16

While this code snippet may solve the question, [including an explanation](http://meta.stackexchange.com/questions/114762/explaining-entirely-code-based-answers) really helps to improve the quality of your post. Remember that you are answering the question for readers in the future, and those people might not know the reasons for your code suggestion. – Clijsters Mar 09 '18 at 13:02

score 0 · Answer 3 · answered Apr 04 '23 at 08:42

I had the same question recently, what worked for me was to do the following:

const express = require('express');
const app = express();
const port = 3000;
let options = {
  maxAge: '2y',
  etag: false
}

app.use(express.static('public', options));

Basically with maxAge you set your cache time. Documentation: https://expressjs.com/en/starter/static-files.html

Cache Control for Dynamic Data Express.JS

3 Answers3

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