GraphQL.js is a general-purpose library and can be used both in a Node server and in the browser. As an example, the GraphiQL tool is built with GraphQL.js!
Building a project using GraphQL.js with webpack or rollup should just work and only include the portions of the library you use. This works because GraphQL.js is distributed with both CommonJS (require()) and ESModule (import) files. Ensure that any custom build configurations look for .mjs files!