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Runtime Error "require is not defined" when bundling with webpack

See original GitHub issue

When bundling graphiql with webpack, you get this error at runtime:

ReferenceError: require is not defined
    at Module.../sourcegraph/node_modules/graphql/jsutils/instanceOf.mjs (instanceOf.mjs:28)
    at __webpack_require__ (bootstrap:63)
    at Module.../sourcegraph/node_modules/graphql/type/definition.mjs (definition.mjs:1)
    at __webpack_require__ (bootstrap:63)
    at Module.../sourcegraph/node_modules/graphql/type/validate.mjs (validate.mjs:1)
    at __webpack_require__ (bootstrap:63)
    at Module.../sourcegraph/node_modules/graphql/graphql.mjs (graphql.mjs:1)
    at __webpack_require__ (bootstrap:63)
    at Module.../sourcegraph/node_modules/graphql/index.mjs (index.mjs:2)
    at __webpack_require__ (bootstrap:63)

This is because instanceOf.js in graphql contains a reference to process.env: https://github.com/graphql/graphql-js/blob/dec24f9/src/jsutils/instanceOf.js#L19-L36

In the ESM build, which is used by webpack by following the module field in package.json, the file gets compiled to a .mjs file, which does not get applied the webpack ProvidePlugin, see https://github.com/webpack/webpack/issues/7032.

This makes it impossible to bundle graphiql with webpack.

Also reported to graphql-js at https://github.com/graphql/graphql-js/issues/1536, but filing here for visibility.