---
title: Fix Vite 8 manualChunks Object Form Removed
description: Fix Vite 8 rejecting object-form manualChunks. Rolldown only supports the function form - here's the real error and the fix.
date: 2026-08-05T00:00:00.000Z
category: guides-fixes
tags: vite, rolldown, config, bug-fix
---

## Quick Answer

Vite 8's Rolldown bundler rejects the object form of `output.manualChunks` outright: "the object form ... is not supported anymore." A real migration tool hit this directly: `Invalid type: Expected Function but received Object`. Rewrite `manualChunks` as a function, the same chunk-splitting logic, just called per module instead of declared as a static map.

## Why the object form stopped working

Rollup's `output.manualChunks` accepted two shapes: a function that gets called once per module and returns the chunk name it belongs to, or a plain object mapping chunk names to arrays of module IDs, a common shorthand for a simple vendor/app split. [Vite's migration guide](https://vite.dev/guide/migration) is direct about what changed: "The object form `output.manualChunks` option is not supported anymore. The function form `output.manualChunks` is deprecated."

Rolldown only implements the function form. The object-map shorthand (arguably the more commonly used of the two, since it's the one most copy-pasted vendor-chunk snippets use) is rejected at build time, not silently ignored:

```
Warning: Invalid output options (1 issue found) - For the 'manualChunks'. Invalid type: Expected Function but received Object.
```

That exact error comes from a real migration tool's own config validator ([voidzero-dev/vite-plus#900](https://github.com/voidzero-dev/vite-plus/issues/900), opened 2026-03-15), hit while trying to convert a project's Rollup-era config to Rolldown. The same shape of error appears in a plain Vite 8 build with an object-form `manualChunks`, not just inside that specific tool.

## Fix it: rewrite as a function

### Before: the object form

```js title="vite.config.ts - Vite 7 pattern"
export default defineConfig({
  build: {
    rollupOptions: {
      output: {
        manualChunks: {
          vendor: ["react", "react-dom"], // BROKEN in Vite 8: object form rejected
        },
      },
    },
  },
});
```

### After: the same split, as a function

```js title="vite.config.ts - Vite 8 pattern"
export default defineConfig({
  build: {
    rollupOptions: {
      output: {
        manualChunks(id) {
          // FIXED: same vendor-chunk logic, called per module
          if (
            id.includes("node_modules/react") ||
            id.includes("node_modules/react-dom")
          ) {
            return "vendor";
          }
        },
      },
    },
  },
});
```

The function receives each module's resolved ID and runs once per module during the build. Returning a string assigns that module to a named chunk; returning nothing leaves Rolldown's default chunking in place for it, the same contract the function form already had under Rollup.

<Callout type="tip" title="Consider skipping manualChunks entirely">
  If your object form was a simple vendor/app split rather than something tuned
  for a specific loading strategy, removing `manualChunks` and letting
  Rolldown's own chunking handle it automatically is a real option, not just a
  fallback. Rolldown also exposes a `codeSplitting` option built for this exact
  case, which is worth checking before porting a complex object map line by line
  into a function.
</Callout>

## Confirmed version range

Confirmed via Rolldown's real-world error output, cited above, against `rolldown@1.0.0-rc.9` and `vite@8.0.0`. Documented as an intentional, permanent removal in Vite's own current migration guide, not a temporary regression. This site's own `astro.config.mjs` doesn't customize `manualChunks` at all, so this specific error wasn't independently reproducible against this repo's own build. Same key rename to check while you're here: [Fix Vite 8's build.rollupOptions Deprecation](/guides-fixes/fix-vite-8-build-rollupoptions-deprecation/) - `manualChunks` is the single most common thing people configure inside that renamed key. Browse more posts like this in the [Guides & Fixes](/guides-fixes) archive.