add relay environment

app/javascript/relay/environment.ts

@@ -0,0 +1,40 @@
+import type { Variables, RequestParameters, CacheConfig } from "relay-runtime";
+import { Environment, Network, RecordSource, Store } from "relay-runtime";
+
+async function fetchRelay(
+  params: RequestParameters,
+  variables: Variables,
+  _cacheConfig: CacheConfig
+) {
+  const response = await fetch("/graphql", {
+    method: "POST",
+    headers: {
+      "Content-Type": "application/json",
+    },
+    body: JSON.stringify({
+      query: params.text,
+      variables,
+    }),
+  });
+
+  const json = await response.json();
+
+  if (Array.isArray(json.errors)) {
+    throw new Error(
+      `Error fetching GraphQL query '${
+        params.name
+      }' with variables '${JSON.stringify(variables)}': ${JSON.stringify(
+        json.errors
+      )}`
+    );
+  }
+
+  return json;
+}
+
+export const environment = new Environment({
+  network: Network.create(fetchRelay),
+  store: new Store(new RecordSource(), {
+    gcReleaseBufferSize: 10,
+  }),
+});