custom-server-only

This package is a server-only alternative that library authors can use to customise the error message.

Why?

server-only and client-only are great if you use it in your own apps. If it's imported in a third party library however, the error message is not so clear to debug anymore.

For example, say I make a library where a particular module must be client-only. If you use the module in a server environment, you get

This module cannot be imported from a Server Component module. It should only be used from a Client Component.

Since you didn't use client-only explicitly, you are left wondering what does "this module" refer to here.

With custom-server-only and custom-client-only here however, I can customise it to something like

"my-package/use-window-size" cannot be used in a server component. Please use a client component instead. Refer to https://my-package.js.org/use-window-size for more info.

which makes it easier for library users to debug.

Usage

Before:

import "server-only";

After:

import ensureServer from "custom-server-only";
ensureServer("Error message here");

If you want to use the default error message instead, use ensureServer(). (But why don't you use server-only directly in that case?)

See also custom-client-only.