cdn-cache-control

Easy, opinionated CDN cache header handling.

Modern CDNs allow very fine-grained control over the cache. This is particularly useful for server-side rendering of web content, as it allows you to manually handle the invalidation of content, ensuring it stays fast and fresh. This package provides a subclass of the Headers class that makes it easier to set cache control headers for content served through a modern CDN. It provides a simple, chainable API with sensible defaults for common use cases. It works by setting the Cache-Control and CDN-Cache-Control headers to the appropriate values. If run on a supported platform it will use the more specific header for that CDN. e.g. on Netlify it will use the Netlify-CDN-Cache-Control header.

e.g.

// Expires in 1 minute, but use stale-while-revalidate to serve stale content after that
const headers = new CacheHeaders().ttl(ONE_MINUTE).swr();

Installation

npm install cdn-cache-control

It is also available in jsr as @ascorbic/cdn-cache-control. If using Deno, you can import it directly without installing:

import { CacheHeaders } from "jsr:@ascorbic/cdn-cache-control";

Usage

The module exports a single class, CacheHeaders, which is a subclass of the fetch Headers class. It provides a chainable API for setting cache headers. By default it sets the Cache-Control and CDN-Cache-Control headers to sensible defaults for content that should be cached by the CDN and revalidated by the browser.

It can be instantiated with a HeadersInit value, which lets you base it on an existing Headers object, or an object or array with existing header values. In that case it will default to using existing s-maxage directives if present.

Use cases

If you have content that you want to have the CDN cache until it is manually revalidated or purged with a new deploy, you can use the default values:

import { CacheHeaders } from "cdn-cache-control";

const headers = new CacheHeaders();

This sets the CDN-Cache-Control header to public,s-maxage=31536000,must-revalidate, which tells the CDN to cache the content for a year. It sets Cache-Control to public,max-age=0,must-revalidate, which tells the browser to always check with the CDN for a fresh version. You should combine this with an ETag or Last-Modified header to allow the CDN to serve a 304 Not Modified response when the content hasn't changed.

stale-while-revalidate

You can enable stale-while-revalidate with the swr method, optionally passing a value for the time to serve stale content (defaults to one week):

import { CacheHeaders } from "cdn-cache-control";

const headers = new CacheHeaders().swr();

This tells the CDN to serve stale content while revalidating the content in the background. Combine with the ttl method to set the time for which the content will be considered fresh (default is zero, meaning the CDN will always revalidate):

import { CacheHeaders, ONE_HOUR } from "cdn-cache-control";

const headers = new CacheHeaders().swr().ttl(ONE_HOUR);

Immutable content

If you are serving content that is guaranteed to never change then you can set it as immutable. You should only do this for responses with unique URLs, because there will be no way to invalidate it from the browser cache if it ever changes.

import { CacheHeaders } from "cdn-cache-control";
const headers = new CacheHeaders().immutable();

This will set the CDN and browser caches to expire in 1 year, and add the immutable directive.

Cache tags

Some CDNs support the use of cache tags, which allow you to purge content from the cache in bulk. The tag() function makes it simple to add tags. You can call it with a string or array of strings.

import { CacheHeaders } from "cdn-cache-control";
const headers = new CacheHeaders().tag(["blog", "blog:1"]);

You can then purge the tagged items from the cache using the CDN API. e.g. for Netlify the API is:

import { purgeCache } from "@netlify/functions";

export default async function handler(req: Request) => {
  await purgeCache({
    tags: ["blog", "blog:1", "blog:2"],
  });
  return new Response("Purged!", { status: 202 })
};

Using the generated headers

The headers object can be used anywhere that accepts a fetch Headers object. This includes most serverless hosts. It can also be used directly in many framework SSR functions. Some APIs need a plain object rather than a Headers object. For these you can use the toObject() method, which returns a plain object with the header names and values.

import { CacheHeaders } from "cdn-cache-control";

export default async function handler(request: Request): Promise<Response> {
  const headers = new CacheHeaders().swr();
  // The `Response` constructor accepts the object directly
  return new Response("Hello", { headers });
}

Some frameworks use a readonly Response object, so you need to use an existing headers object. In this case you can use the copyTo method to copy the headers to the response:

---
import { CacheHeaders, ONE_HOUR } from "cdn-cache-control";

new CacheHeaders().swr(ONE_HOUR).copyTo(Astro.response.headers);
---

API

⚙️ ONE_MINUTE

Number of seconds in one minute

Constant	Type
`ONE_MINUTE`	`60`

⚙️ ONE_HOUR

Number of seconds in one hour

Constant	Type
`ONE_HOUR`	`3600`

⚙️ ONE_DAY

Number of seconds in one day

Constant	Type
`ONE_DAY`	`86400`

⚙️ ONE_WEEK

Number of seconds in one week

Constant	Type
`ONE_WEEK`	`604800`

⚙️ ONE_YEAR

Number of seconds in one year

Constant	Type
`ONE_YEAR`	`31536000`

🏭 CacheHeaders

Methods

tag
swr
immutable
ttl
toObject
copyTo
getCdnCacheControl
setCdnCacheControl
getCacheControl
setCacheControl
getCacheTags
setCacheTags

⚙️ tag

Adds a cache tag to the cache tags header. Cache tags are used to invalidate the cache for a URL.

Method	Type
`tag`	`(tag: string or string[], ...tags: string[]) => this`

Parameters:

tag: The cache tag to add. Can be a string or an array of strings.

⚙️ swr

Sets stale-while-revalidate directive for the CDN cache. By default the browser is sent a must-revalidate directive to ensure that the browser always revalidates the cache with the server.

Method	Type
`swr`	`(value?: number) => this`

Parameters:

value: The number of seconds to set the stale-while-revalidate directive to. Defaults to 1 week.

⚙️ immutable

Sets cache headers for content that should be cached for a long time and never revalidated. The CDN cache will cache the content for the specified time, and the browser will cache the content indefinitely without revalidating. Do not use this unless the URL is fingerprinted or otherwise unique. Otherwise, the browser will cache the content indefinitely and never check for updates, including for new deploys.

Method	Type
`immutable`	`(value?: number) => this`

Parameters:

value: The number of seconds to set the CDN cache-control s-maxage directive to. Defaults to 1 year.

⚙️ ttl

Sets the s-maxage for items in the CDN cache. This is the maximum amount of time that the CDN will cache the content. If used with swr, the content will revalidate in the background after the max age has passed. Otherwise, the content will be removed from the cache after the max age has passed.

Method	Type
`ttl`	`(value: number) => this`

⚙️ toObject

Returns the headers as a plain object.

Method	Type
`toObject`	`() => Record<string, string>`

⚙️ copyTo

Copy the headers from this instance to another Headers instance.

Method	Type
`copyTo`	`<T extends Headers>(headers: T) => T`

⚙️ getCdnCacheControl

The parsed cache-control header for the CDN cache.

Method	Type
`getCdnCacheControl`	`() => Record<string, string>`

⚙️ setCdnCacheControl

Method	Type
`setCdnCacheControl`	`(directives: Record<string, string>) => void`

⚙️ getCacheControl

The parsed cache-control header for the browser cache.

Method	Type
`getCacheControl`	`() => Record<string, string>`

⚙️ setCacheControl

Method	Type
`setCacheControl`	`(directives: Record<string, string>) => void`

⚙️ getCacheTags

The parsed content of the cache tags header.

Method	Type
`getCacheTags`	`() => string[]`

⚙️ setCacheTags

Method	Type
`setCacheTags`	`(tags: string[]) => void`