Prioritise workerd condition when bundling (#2629)

* Prioritise `workerd` condition when bundling

Ref: https://runtime-keys.proposal.wintercg.org/#workerd

* fixup! Prioritise `workerd` condition when bundling

* fixup! Prioritise `workerd` condition when bundling

* fixup! Prioritise `workerd` condition when bundling

.changeset/chilly-donuts-fetch.md

@@ -0,0 +1,10 @@
+---
+"wrangler": minor
+---
+
+Prefer the `workerd` `exports` condition when bundling.
+
+This can be used to build isomorphic libraries that have different implementations depending on the JavaScript runtime they're running in.
+When bundling, Wrangler will try to load the [`workerd` key](https://runtime-keys.proposal.wintercg.org/#workerd).
+This is the [standard key](https://runtime-keys.proposal.wintercg.org/#workerd) for the Cloudflare Workers runtime.
+Learn more about the [conditional `exports` field here](https://nodejs.org/api/packages.html#conditional-exports).

fixtures/isomorphic-random-example/README.md

@@ -0,0 +1,7 @@
+# Isomorphic Package Example
+
+This package implements an isomorphic library that generates cryptographically-strong pseudorandom numbers.
+What this package does isn't really important here, the key part is the [`package.json`](./package.json)'s `exports` field.
+Conditional exports provide a way to load a different file depending on where the module is being imported from.
+By default, Wrangler will try to look for a [**`workerd`** key](https://runtime-keys.proposal.wintercg.org/#workerd).
+This allows you as a library developer to implement different behaviour for different JavaScript runtimes.

fixtures/isomorphic-random-example/package.json

@@ -0,0 +1,10 @@
+{
+	"name": "isomorphic-random-example",
+	"version": "0.0.1",
+	"private": true,
+	"description": "Isomorphic secure-random library, demonstrating `exports` use with Workers",
+	"exports": {
+		"node": "./src/node.js",
+		"workerd": "./src/workerd.mjs"
+	}
+}

fixtures/isomorphic-random-example/src/node.js

@@ -0,0 +1,5 @@
+const crypto = require("node:crypto");
+
+module.exports.randomBytes = function (length) {
+	return new Uint8Array(crypto.randomBytes(length));
+};

fixtures/isomorphic-random-example/src/workerd.mjs

@@ -0,0 +1,3 @@
+export function randomBytes(length) {
+	return crypto.getRandomValues(new Uint8Array(length));
+}

fixtures/worker-app/src/index.js

@@ -1,6 +1,18 @@
 import { now } from "./dep";
+import { randomBytes } from "isomorphic-random-example";
+
+/** @param {Uint8Array} array */
+function hexEncode(array) {
+	return Array.from(array)
+		.map((x) => x.toString(16).padStart(2, "0"))
+		.join("");
+}
+
 export default {
 	async fetch(request) {
+		const { pathname } = new URL(request.url);
+		if (pathname === "/random") return new Response(hexEncode(randomBytes(8)));
+
 		console.log(
 			request.method,
 			request.url,

fixtures/worker-app/tests/index.test.ts

@@ -20,4 +20,10 @@ describe.concurrent("'wrangler dev' correctly renders pages", () => {
 		const text = await response.text();
 		expect(text).toContain(`http://${ip}:${port}/`);
 	});
+
+	it("uses `workerd` condition when bundling", async ({ expect }) => {
+		const response = await fetch(`http://${ip}:${port}/random`);
+		const text = await response.text();
+		expect(text).toMatch(/[0-9a-f]{16}/); // 8 hex bytes
+	});
 });

packages/wrangler/src/bundle.ts

@@ -340,7 +340,7 @@ export async function bundleWorker(
 		sourceRoot: destination,
 		minify,
 		metafile: true,
-		conditions: ["worker", "browser"],
+		conditions: ["workerd", "worker", "browser"],
 		...(process.env.NODE_ENV && {
 			define: {
 				// use process.env["NODE_ENV" + ""] so that esbuild doesn't replace it