How to read JSON with Next.js 13 API routes

tldr;

const data = await request.json()

The Request Object

Next.js 13 has support for API routes in the app directory. These routes have a new function signature:

export async function GET(request: Request) {
  // do things here
  return Response.json({ hello: 'world' })
}

The Request object is a standard web request (docs). The body property is a read-only ReadableStream, which you could use, but it's not elegant. Instead, you want to use the helper methods the Request object provides to parse the data:

• Request.arrayBuffer() - Returns a promise that resolves with an ArrayBuffer representation of the request body.
• Request.blob() - Returns a promise that resolves with a Blob representation of the request body.
• Request.formData() - Returns a promise that resolves with a FormData representation of the request body.
• Request.json() - Returns a promise that resolves with the result of parsing the request body as JSON.
• Request.text() - Returns a promise that resolves with a text representation of the request body.

Each of these methods returns a Promise, so ensure you await the result before you use it.