From 146acb15130f096c9120f29dca511391ee9994f1 Mon Sep 17 00:00:00 2001
From: Manu MA <manu.mtza@gmail.com>
Date: Tue, 8 Feb 2022 15:21:09 +0000
Subject: [PATCH] feat: add ssr.format to force esm output for ssr

---
 packages/vite/src/node/build.ts  | 5 +++--
 packages/vite/src/node/config.ts | 6 ++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/packages/vite/src/node/build.ts b/packages/vite/src/node/build.ts
index 7c7d1d18037174..279a05c1313045 100644
--- a/packages/vite/src/node/build.ts
+++ b/packages/vite/src/node/build.ts
@@ -367,6 +367,7 @@ async function doBuild(
   const config = await resolveConfig(inlineConfig, 'build', 'production')
   const options = config.build
   const ssr = !!options.ssr
+  const esm = config.ssr?.format === 'es' || !ssr
   const libOptions = options.lib
 
   config.logger.info(
@@ -464,8 +465,8 @@ async function doBuild(
 
       return {
         dir: outDir,
-        format: ssr ? 'cjs' : 'es',
-        exports: ssr ? 'named' : 'auto',
+        format: esm ? 'es' : 'cjs',
+        exports: esm ? 'auto' : 'named',
         sourcemap: options.sourcemap,
         name: libOptions ? libOptions.name : undefined,
         entryFileNames: ssr
diff --git a/packages/vite/src/node/config.ts b/packages/vite/src/node/config.ts
index f73f4fb8662d6b..cc0ace3ef3d708 100644
--- a/packages/vite/src/node/config.ts
+++ b/packages/vite/src/node/config.ts
@@ -221,6 +221,12 @@ export interface SSROptions {
    * Default: 'node'
    */
   target?: SSRTarget
+
+  /**
+   * Define the module format for the ssr build.
+   * Default: 'cjs'
+   */
+  format?: 'es' | 'cjs'
 }
 
 export interface ResolveWorkerOptions {