Cache

Nitro provides a caching system built on top of the storage layer.

#Cached event handlers

To cache an event handler, you simply need to use the defineCachedEventHandler method.

It works like defineEventHandler but with an additional second options parameter.

server/routes/cached.ts

// Cache an API handler
export default defineCachedEventHandler((event) => {
  // My event handler
}, { maxAge: 60 * 60 /* 1 hour */ });

With this example, the response will be cached for 1 hour and a stale value will be sent to the client while the cache is being updated in the background. If you want to immediately return the updated response set swr: false.

Important

All incoming request headers are dropped when handling cached responses. If you define the varies option, only the specified headers will be considered when caching and serving the responses.

See the options section for more details about the available options.

Note

You can also use the cachedEventHandler method as alias of defineCachedEventHandler.

#Cached functions

You can also cache a function using the defineCachedFunction function. This is useful for caching the result of a function that is not an event handler, but is part of one, and reusing it in multiple handlers.

For example, you might want to cache the result of an API call for one hour:

export const cachedGHStars = defineCachedFunction(async (repo: string) => {
  const data: any = await $fetch(`https://api.github.com/repos/${repo}`)

  return data.stargazers_count
}, {
  maxAge: 60 * 60,
  name: 'ghStars',
  getKey: (repo: string) => repo
})

The stars will be cached in development inside .nitro/cache/functions/ghStars/<owner>/<repo>.json with value being the number of stars.

{"expires":1677851092249,"value":43991,"mtime":1677847492540,"integrity":"ZUHcsxCWEH"}

Important

Because the cached data is serialized to JSON, it is important that the cached function does not return anything that cannot be serialized, such as Symbols, Maps, Sets…

Note

You can also use the cachedFunction method as alias of defineCachedFunction.

#Edge workers

In edge workers, the instance is destroyed after each request. Nitro automatically uses event.waitUntil to keep the instance alive while the cache is being updated while the response is sent to the client.

To ensure that your cached functions work as expected in edge workers, you should always pass the event as the first argument to the function using defineCachedFunction.

import type { H3Event } from 'h3'

export const cachedGHStars = defineCachedFunction(async (event: H3Event, repo: string) => {
  const data: any = await $fetch(`https://api.github.com/repos/${repo}`)

  return data.stargazers_count
}, {
  maxAge: 60 * 60,
  name: 'ghStars',
  getKey: (event: H3Event, repo: string) => repo
})

This way, the function will be able to keep the instance alive while the cache is being updated without slowing down the response to the client.

#Caching route rules

This feature enables you to add caching routes based on a glob pattern directly in the main configuration file. This is especially useful to have a global cache strategy for a part of your application.

Cache all the blog routes for 1 hour with stale-while-revalidate behavior:

export default defineNitroConfig({
  routeRules: {
    "/blog/**": { cache: { maxAge: 60 * 60 } },
  },
});

If we want to use a custom storage mount point, we can use the base option.

export default defineNitroConfig({
  storage: {
    redis: {
      driver: "redis",
      url: "redis://localhost:6379",
    },
  },
  routeRules: {
    "/blog/**": { cache: { maxAge: 60 * 60, base: "redis" } },
  },
});

#Customize cache storage

Nitro stores the data in the cache: mount point.

In production, it will use the memory driver by default.
In development, it will use the filesystem driver, writing to a temporary dir.

To overwrite the production storage, set the cache mount point using the storage option:

export default defineNitroConfig({
  storage: {
    cache: {
      driver: 'redis',
      /* redis connector options */
    }
  }
})

In development, you can also overwrite the cache mount point using the devStorage option:

export default defineNitroConfig({
  devStorage: {
    cache: {
      driver: 'redis',
      /* redis connector options */
    }
  }
})

#Options

The cachedEventHandler and cachedFunction functions accept the following options:

Name of the storage mountpoint to use for caching. :br Default to cache.

Guessed from function name if not provided, and falls back to '_' otherwise.

Defaults to 'nitro/handlers' for handlers and 'nitro/functions' for functions.

A function that accepts the same arguments as the original function and returns a cache key (String). :br If not provided, a built-in hash function will be used to generate a key based on the function arguments.

A value that invalidates the cache when changed. :br By default, it is computed from function code, used in development to invalidate the cache when the function code changes.

Maximum age that cache is valid, in seconds. :br Default to 1 (second).

Maximum age that a stale cache is valid, in seconds. If set to -1 a stale value will still be sent to the client while the cache updates in the background. :br Defaults to 0 (disabled).

Enable stale-while-revalidate behavior to serve a stale cached response while asynchronously revalidating it. :br Defaults to true.

A function that returns a boolean to invalidate the current cache and create a new one.

A function that returns a boolean to bypass the current cache without invalidating the existing entry.

An array of request headers to be considered for the cache, learn more. If utilizing in a multi-tenant environment, you may want to pass ['host', 'x-forwarded-host'] to ensure these headers are not discarded and that the cache is unique per tenant.

#Cache keys and invalidation

When using the defineCachedFunction or defineCachedEventHandler functions, the cache key is generated using the following pattern:

`${options.group}:${options.name}:${options.getKey(...args)}.json`

For example, the following function:

const getAccessToken = defineCachedFunction(() => {
  return String(Date.now())
}, {
  maxAge: 10,
  name: 'getAccessToken',
  getKey: () => 'default'
})

Will generate the following cache key:

nitro:functions:getAccessToken:default.json

You can invalidate the cached function entry with:

await useStorage('cache').removeItem('nitro:functions:getAccessToken:default.json')

#Normalizing Cache Keys

Important

Cache keys are automatically normalized using an internal utility that removes non-alphanumeric characters such as / and -. This behavior helps ensure compatibility across various storage backends (e.g., file systems, key-value stores) that might have restrictions on characters in keys, and also prevents potential path traversal vulnerabilities.

For example:

getKey: () => '/api/products/sale-items'

Would generate a key like:

api/productssaleitems.json

This behavior may result in keys that look different from the original route or identifier.

Tip

To manually reproduce the same normalized key pattern used by Nitro (e.g., when invalidating cache entries), you can use the escapeKey utility function provided below:

function escapeKey(key: string | string[]) {
  return String(key).replace(/\W/g, "");
}

It's recommended to use escapeKey() when invalidating manually using route paths or identifiers to ensure consistency with Nitro's internal key generation.

For example, if your getKey function is:

getKey: (id: string) => `product/${id}/details`

And you want to invalidate product/123/details, you would do:

const normalizedKey = escapeKey('product/123/details')
await useStorage('cache').removeItem(`nitro:functions:getProductDetails:${normalizedKey}.json`)

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