Is @graphiql/toolkit ESM or not?

[s100]

After running npm install @graphiql/toolkit I see a directory esm and inside that I see numerous *.js files with the compiled code of the package. These source files use ES Modules syntax (import and export). Good stuff. But midway through esm/create-fetcher/lib.js is this line:

graphiql/packages/graphiql-toolkit/src/create-fetcher/lib.ts

Lines 77 to 79 in 88ae243

	const { createClient } = require('graphql-ws') as {
	createClient: typeof createClientType;
	};

So is this an ES module or not? Please could you explain what's going on here. This causes a ReferenceError, surely?