fix: NPM bundling should use ESM format (#494)

* chore: show how top-level await can throw esbuild off

* fix: specify ESM format

node/bundler.test.ts

@@ -486,6 +486,7 @@ test('Handles imports with the `node:` prefix', async () => {
 })
 
 test('Loads npm modules from bare specifiers', async () => {
+  const systemLogger = vi.fn()
   const { basePath, cleanup, distPath } = await useFixture('imports_npm_module')
   const sourceDirectory = join(basePath, 'functions')
   const declarations: Declaration[] = [
@@ -501,7 +502,13 @@ test('Loads npm modules from bare specifiers', async () => {
     featureFlags: { edge_functions_npm_modules: true },
     importMapPaths: [join(basePath, 'import_map.json')],
     vendorDirectory: vendorDirectory.path,
+    systemLogger,
   })
+
+  expect(
+    systemLogger.mock.calls.find((call) => call[0] === 'Could not track dependencies in edge function:'),
+  ).toBeUndefined()
+
   const manifestFile = await readFile(resolve(distPath, 'manifest.json'), 'utf8')
   const manifest = JSON.parse(manifestFile)
   const bundlePath = join(distPath, manifest.bundles[0].asset)

node/npm_dependencies.ts

@@ -148,6 +148,7 @@ export const vendorNPMSpecifiers = async ({
       platform: 'node',
       plugins: [getDependencyTrackerPlugin(specifiers, importMap.getContentsWithURLObjects(), pathToFileURL(basePath))],
       write: false,
+      format: 'esm',
     })
   } catch (error) {
     logger.system('Could not track dependencies in edge function:', error)

test/fixtures/imports_npm_module/functions/func1.ts

@@ -3,6 +3,8 @@ import parent2 from 'parent-2'
 import parent3 from './lib/util.ts'
 import { echo } from 'alias:helper'
 
+await Promise.resolve()
+
 export default async () => {
   const text = [parent1('JavaScript'), parent2('APIs'), parent3('Markup')].join(', ')