graphql-js: "one instance of graphql" error when using esm package.

This happens if you were to add a new npm script called

"mjsImport": "node --experimental-modules serverWithImport.mjs"

and a test file serverWithImport.mjs:

import graphglYoga from 'graphql-yoga';
import { GraphQLObjectType, GraphQLSchema, GraphQLString } from "graphql";

const { GraphQLServer } = graphglYoga

var Something = new GraphQLObjectType({
    fields: {
        else: { type: GraphQLString },
    },
    name: 'Something',
})

var schema = new GraphQLSchema({
    query: new GraphQLObjectType({
        fields: {
            something: {
                type: Something,
            },
        },
        name: 'Query',
    }),
});

var server = new GraphQLServer({ schema });
const instance = server.start(); // defaults to port 4000

too.

The issue is that graphql-yoga is CJS (and loads the CJS entry of graphql) but you’re loading the ESM version of graphql.

Because graphgl is running two entry points they create 2 separate instances (a limitation of their current dual approach). The way around it is for graphql to instantiate their instances in CJS and export them for the ESM entry to consume.