Dynamic APIs are Asynchronous

Learn more about why accessing certain APIs synchronously now warns.

Why This Warning Occurred

Somewhere in your code you used an API that opts into dynamic rendering.

Dynamic APIs are:

• The params and searchParams props that get provided to pages, layouts, metadata APIs, and route handlers.
• cookies(), draftMode(), and headers() from next/headers

In Next 15, these APIs have been made asynchronous. You can read more about this in the Next.js 15 Upgrade Guide.

For example, the following code will issue a warning:

function Page({ params }) {
  // direct access of `params.id`.
  return <p>ID: {params.id}</p>
}

This also includes enumerating (e.g. {...params}, or Object.keys(params)) or iterating over the return value of these APIs (e.g. [...headers()] or for (const cookie of cookies()), or explicitly with cookies()[Symbol.iterator]()).

In the version of Next.js that issued this warning, access to these properties is still possible directly but will warn. In future versions, these APIs will be async and direct access will not work as expected.

Possible Ways to Fix It

The next-async-request-api codemod can fix many of these cases automatically:

$ npx @next/codemod@canary next-async-request-api .

The codemod cannot cover all cases, so you may need to manually adjust some code.

If the warning occured on the Server (e.g. a route handler, or a Server Component), you must await the dynamic API to access its properties:

async function Page({ params }) {
  // asynchronous access of `params.id`.
  const { id } = await params
  return <p>ID: {id}</p>
}

If the warning occured in a synchronous component (e.g. a Client component), you must use React.use() to unwrap the Promise first:

'use client'
import * as React from 'react'
 
function Page({ params }) {
  // asynchronous access of `params.id`.
  const { id } = React.use(params)
  return <p>ID: {id}</p>
}

Unmigratable Cases

If Next.js codemod found anything that is not able to be migrated by the codemod, it will leave a comment with @next-codemod-error prefix and the suggested action, for example: In this case, you need to manually await the call to cookies(), and change the function to async. Then refactor the usages of the function to be properly awaited:

export function MyCookiesComponent() {
  const c =
    /* @next-codemod-error Manually await this call and refactor the function to be async */
    cookies()
  return c.get('name')
}

Enforced Migration with Linter

If you didn't address the comments that starting with @next-codemod-error left by the codemod, Next.js will error in both dev and build to enforce you to address the issues. You can review the changes and follow the suggestion in the comments. You can either make the necessary changes and remove the comment, or replace the comment prefix @next-codemod-error with @next-codemod-ignore If there's no action to be taken, the comment prefix @next-codemod-ignore will bypass the build error.

- /* @next-codemod-error <suggested message> */
+ /* @next-codemod-ignore */

Good to know:

You can delay unwrapping the Promise (either with await or React.use) until you actually need to consume the value. This will allow Next.js to statically render more of your page.