fix(resolve)!: remove special .mjs handling (#14723)

Author: bluwy

docs/guide/migration.md

@@ -133,6 +133,8 @@ Also there are other breaking changes which only affect few users.
   - Renamed `ResolveWorkerOptions` type to `ResolvedWorkerOptions`
 - [[#5657] fix: return 404 for resources requests outside the base path](https://github.com/vitejs/vite/pull/5657)
   - In the past, Vite responded to requests outside the base path without `Accept: text/html`, as if they were requested with the base path. Vite no longer does that and responds with 404 instead.
+- [[#14723] fix(resolve)!: remove special .mjs handling](https://github.com/vitejs/vite/pull/14723)
+  - In the past, when a library `"exports"` field maps to an `.mjs` file, Vite will still try to match the `"browser"` and `"module"` fields to fix compatibility with certain libraries. This behavior is now removed to align with the exports resolution algorithm.
 
 ## Migration from v3
 

packages/vite/src/node/plugins/resolve.ts

@@ -987,17 +987,8 @@ export function resolvePackageEntry(
       )
     }
 
-    const resolvedFromExports = !!entryPoint
-
-    // if exports resolved to .mjs, still resolve other fields.
-    // This is because .mjs files can technically import .cjs files which would
-    // make them invalid for pure ESM environments - so if other module/browser
-    // fields are present, prioritize those instead.
-    if (
-      targetWeb &&
-      options.browserField &&
-      (!entryPoint || entryPoint.endsWith('.mjs'))
-    ) {
+    // handle edge case with browser and module field semantics
+    if (!entryPoint && targetWeb && options.browserField) {
       // check browser field
       // https://github.com/defunctzombie/package-browser-field-spec
       const browserEntry =
@@ -1039,8 +1030,7 @@ export function resolvePackageEntry(
     }
 
     // fallback to mainFields if still not resolved
-    // TODO: review if `.mjs` check is still needed
-    if (!resolvedFromExports && (!entryPoint || entryPoint.endsWith('.mjs'))) {
+    if (!entryPoint) {
       for (const field of options.mainFields) {
         if (field === 'browser') continue // already checked above
         if (typeof data[field] === 'string') {