Throw TypeError on Fetcher#fetch illegal invocation

Author: mrbbot

packages/core/src/plugins/bindings.ts

@@ -87,6 +87,10 @@ export class Fetcher {
   }
 
   async fetch(input: RequestInfo, init?: RequestInit): Promise<Response> {
+    if (!(this instanceof Fetcher)) {
+      throw new TypeError("Illegal invocation");
+    }
+
     // Always create new Request instance, so clean object passed to services
     const req = new Request(input, init);
 

packages/core/test/plugins/bindings.spec.ts

@@ -540,6 +540,18 @@ test("Fetcher: hides implementation details", (t) => {
   const fetcher = new Fetcher(throws, throws);
   t.deepEqual(getObjectProperties(fetcher), ["fetch"]);
 });
+test("Fetcher: fetch: throws on illegal invocation", async (t) => {
+  const throws = () => {
+    throw new Error("Should not be called");
+  };
+  const fetcher = new Fetcher(throws, throws);
+  // @ts-expect-error using comma expression to unbind this
+  // noinspection CommaExpressionJS
+  await t.throwsAsync(() => (0, fetcher.fetch)("http://localhost"), {
+    instanceOf: TypeError,
+    message: "Illegal invocation",
+  });
+});
 test("BindingsPlugin: dispatches fetch to mounted service", async (t) => {
   const mf = useMiniflare(
     { BindingsPlugin },