fix: bundle worker as iife if detected as a service worker (#941)

.changeset/good-geese-matter.md

@@ -0,0 +1,11 @@
+---
+"wrangler": patch
+---
+
+fix: bundle worker as iife if detected as a service worker
+
+We detect whether a worker is a "modules" format worker by the presence of a `default` export. This is a pretty good heuristic overall, but sometimes folks can make mistakes. One situation that's popped up a few times, is people writing exports, but still writing it in "service worker" format. We detect this fine, and log a warning about the exports, but send it up with the exports included. Unfortunately, our runtime throws when we mark a worker as a service worker, but still has exports. This patch fixes it so that the exports are not included in a service-worker worker.
+
+Note that if you're missing an event listener, it'll still error with "No event handlers were registered. This script does nothing." but that's a better error than the SyntaxError _even when the listener was there_.
+
+Fixes https://github.com/cloudflare/wrangler2/issues/937

packages/wrangler/src/__tests__/publish.test.ts

@@ -1,6 +1,7 @@
 import * as fs from "node:fs";
 import * as path from "node:path";
 import * as TOML from "@iarna/toml";
+import * as esbuild from "esbuild";
 import { writeAuthConfigFile } from "../user";
 import { mockAccountId, mockApiToken } from "./helpers/mock-account-id";
 import {
@@ -878,6 +879,77 @@ export default{
       expect(std.err).toMatchInlineSnapshot(`""`);
     });
 
+    it("should preserve exports on a module format worker", async () => {
+      writeWranglerToml();
+      fs.writeFileSync(
+        "index.js",
+        `
+export const abc = 123;
+export const def = "show me the money";
+export default {};`
+      );
+
+      await runWrangler("publish index.js --dry-run --outdir out");
+
+      expect(
+        (
+          await esbuild.build({
+            entryPoints: [path.resolve("./out/index.js")],
+            metafile: true,
+            write: false,
+          })
+        ).metafile?.outputs["index.js"].exports
+      ).toMatchInlineSnapshot(`
+        Array [
+          "abc",
+          "def",
+          "default",
+        ]
+      `);
+      expect(std).toMatchInlineSnapshot(`
+        Object {
+          "debug": "",
+          "err": "",
+          "out": "--dry-run: exiting now.",
+          "warn": "",
+        }
+      `);
+    });
+
+    it("should not preserve exports on a service-worker format worker", async () => {
+      writeWranglerToml();
+      fs.writeFileSync(
+        "index.js",
+        `
+export const abc = 123;
+export const def = "show me the money";
+addEventListener('fetch', event => {});`
+      );
+
+      await runWrangler("publish index.js --dry-run --outdir out --minify");
+
+      expect(
+        (
+          await esbuild.build({
+            entryPoints: [path.resolve("./out/index.js")],
+            metafile: true,
+            write: false,
+          })
+        ).metafile?.outputs["index.js"].exports
+      ).toMatchInlineSnapshot(`Array []`);
+
+      expect(std).toMatchInlineSnapshot(`
+        Object {
+          "debug": "",
+          "err": "",
+          "out": "--dry-run: exiting now.",
+          "warn": "▲ [WARNING] The entrypoint index.js has exports like an ES Module, but hasn't defined a default export like a module worker normally would. Building the worker using \\"service-worker\\" format...
+
+        ",
+        }
+      `);
+    });
+
     it("should be able to transpile entry-points in sub-directories (sw)", async () => {
       writeWranglerToml();
       writeWorkerSource({ basePath: "./src", type: "sw" });

packages/wrangler/src/bundle.ts

@@ -66,7 +66,7 @@ export async function bundleWorker(
     absWorkingDir: entry.directory,
     outdir: destination,
     external: ["__STATIC_CONTENT_MANIFEST"],
-    format: "esm",
+    format: entry.format === "modules" ? "esm" : "iife",
     target: "es2020",
     sourcemap: true,
     minify,