Edge CORS

Enables CORS at the edge, works for Vercel Edge Functions (With the recently announced Next.js Middleware), Deno, Cloudflare Workers, and any environment with Web APIs support, specifically the Fetch API.

This module is a modified version of expressjs/cors, which works for Node.js and should be your way to go if you're looking for Node.js support.

How to use

The module is available in npm, and as a Deno module. To install it from npm:

npm i edge-cors

And to use it in Deno:

import cors from 'https://deno.land/x/edge_cors/src/cors.ts'

Basic Usage in Next.js

import type { NextRequest } from 'next/server'
import cors from 'edge-cors'

export function middleware(req: NextRequest) {
  // `cors` also takes care of handling OPTIONS requests
  return cors(
    req,
    new Response(JSON.stringify({ message: 'Hello World!' }), {
      status: 200,
      headers: { 'Content-Type': 'application/json' },
    })
  )
}

The full example is available in examples/next, and a live demo in Vercel Examples.

Basic Usage in Deno

import { listenAndServe } from 'https://deno.land/std/http/server.ts'
import cors from 'https://deno.land/x/edge_cors/src/cors.ts'

console.log('Listening on http://localhost:8080')

await listenAndServe(':8080', (req) => {
  // `cors` also takes care of handling OPTIONS requests
  return cors(
    req,
    new Response(JSON.stringify({ message: 'Hello World!' }), {
      status: 200,
      headers: { 'Content-Type': 'application/json' },
    })
  )
})

The full example is available in examples/deno.

The signature of the cors function is the following:

function cors(
  req: Request,
  res: Response,
  options?: CorsOptions | undefined
): Promise<Response>

For reference, the types used in the definition are linked below:

• Request
• Response
• CorsOptions

CORS Options

Defined as CorsOptions in src/cors.ts, including JSDoc comments with the same docs from below. Defaults to:

{
  origin: '*',
  methods: 'GET,HEAD,PUT,PATCH,POST,DELETE',
  preflightContinue: false,
  optionsSuccessStatus: 204,
}

origin

The value to match against the Access-Control-Allow-Origin header in the request. Defaults to '*'.

It can be a boolean, string, a regular expression, an array of those, or a function that returns one of those.

If set to '*' all origins will be allowed.

If set to true then Access-Control-Allow-Origin will reflect the origin of the request.

If set to false then all origins will be denied (Access-Control-Allow-Origin will not be set).

If set to a regular expression then the request origin will be matched against it.

If set to a function, it will receive the request origin string as the first parameter and the request as the second parameter. It can return a promise.

methods

Customizes the Access-Control-Allow-Methods header.

It can be a string or an array of strings. Defaults to 'GET,HEAD,PUT,PATCH,POST,DELETE'.

allowedHeaders

Configures the Access-Control-Allow-Headers header.

It can be a string or an array of strings. There's no default value (the header is omitted).

exposedHeaders

Configures the Access-Control-Expose-Headers header.

It can be a string or an array of strings. There's no default value (the header is omitted).

credentials

Configures the Access-Control-Allow-Credentials header.

It can be a boolean. But the header is only set if it is true. There's no default value (the header is omitted).

maxAge

Configures the Access-Control-Max-Age header.

Its value has to be an integer. There's no default value (the header is omitted).

preflightContinue

If true, cors will return the response with updated headers.

If false, cors will return a new Response object with the status code set to the value of optionsSuccessStatus and a empty body.

Defaults to false.

optionsSuccessStatus

Status code to use for OPTIONS requests when preflightContinue is disabled.

Defaults to 204.

Contributing

To create a local build of edge-cors run the following:

npm run build

# or

npm run dev

To run the tests:

npm run test

The tests run with Tape and Node.js. You can also cd into the examples and follow their readmes to use the local build there.