DefinitelyTyped/types/relay-runtime/relay-runtime-tests.tsx

import { Environment, Network, RecordSource, Store, ConnectionHandler, ViewerHandler } from "relay-runtime";

const source = new RecordSource();
const store = new Store(source);

// ~~~~~~~~~~~~~~~~~~~~~
// Network Layer
// ~~~~~~~~~~~~~~~~~~~~~
// Define a function that fetches the results of an operation (query/mutation/etc)
// and returns its results as a Promise:
function fetchQuery(operation: any, variables: { [key: string]: string }, cacheConfig: {}) {
    return fetch("/graphql", {
        method: "POST",
        body: JSON.stringify({
            query: operation.text, // GraphQL text from input
            variables,
        }),
    }).then((response: any) => {
        return response.json();
    });
}

// Create a network layer from the fetch function
const network = Network.create(fetchQuery);

// ~~~~~~~~~~~~~~~~~~~~~
// Environment
// ~~~~~~~~~~~~~~~~~~~~~
const environment = new Environment({
    handlerProvider, // Can omit.
    network,
    store,
});

// ~~~~~~~~~~~~~~~~~~~~~
// Handler Provider
// ~~~~~~~~~~~~~~~~~~~~~

function handlerProvider(handle: any) {
    switch (handle) {
        // Augment (or remove from) this list:
        case "connection":
            return ConnectionHandler;
        case "viewer":
            return ViewerHandler;
    }
    throw new Error(`handlerProvider: No handler provided for ${handle}`);
}