next.config.js

is a regular Node.js module, not a JSON file. It gets used by the Next.js server and build phases, and it’s not included in the browser build.

Take a look at the following next.config.js example:

You can also use a function:

Since Next.js 12.1.0, you can use an async function:

The commented lines are the place where you can put the configs allowed by next.config.js, which are defined in this file.

However, none of the configs are required, and it’s not necessary to understand what each config does. Instead, search for the features you need to enable or modify in this section and they will show you what to do.