gatsbyjs/gatsby · error

Unexpected result of config factory. Expected "function", go

Error message

Unexpected result of config factory. Expected "function", got "${typeof pageConfigFn}".

What it means

Thrown by preparePageTemplateConfigs while preloading each page template's SSR/DSG config. After require-ing a component chunk and calling its exported `config()` method, Gatsby expects the return value to be a function (the actual page-config handler). If the template's config export resolves to anything other than a function, Gatsby cannot use it to drive SSR/DSG rendering and aborts. This guards the page-config contract introduced for server-side rendering modes.

Source

Thrown at packages/gatsby/src/utils/page-mode.ts:135

export async function preparePageTemplateConfigs(
  graphql: Runner
): Promise<void> {
  const { program } = store.getState()
  const pageRendererPath = `${program.directory}/${ROUTES_DIRECTORY}render-page.js`

  const pageRenderer = require(pageRendererPath)
  global[`__gatsbyGraphql`] = graphql

  await Promise.all(
    Array.from(store.getState().components.values()).map(async component => {
      if (component.config) {
        const componentInstance = await pageRenderer.getPageChunk({
          componentChunkName: component.componentChunkName,
        })
        const pageConfigFn = await componentInstance.config()
        if (typeof pageConfigFn !== `function`) {
          throw new Error(
            `Unexpected result of config factory. Expected "function", got "${typeof pageConfigFn}".`
          )
        }

        pageConfigMap.set(component.componentChunkName, pageConfigFn)
      }
    })
  )
  delete global[`__gatsbyGraphql`]
}

View on GitHub (pinned to 8b06340921)

Solutions

1. Open the page template file mapped to the failing componentChunkName and verify its `config` export is `export const config = () => { ... }` (a function returning a function) or uses `import { config } from 'gatsby'`.
2. Check that no plugin or wrapper component is attaching a `config` property that is not the Gatsby config factory.
3. Clear `.cache` and `node_modules` and reinstall to discard stale chunks: `rm -rf .cache node_modules && npm install`.
4. If the error names a `typeof` of `undefined`, confirm the template actually calls the Gatsby-provided `config` helper rather than re-assigning it.

Example fix

// before (page template)
export const config = { render: 'SSR' }

// after
import { config } from 'gatsby'
export const configFactory = config(() => ({ render: 'SSR' }))

// Before relying on a template config, verify its shape
const maybe = componentInstance.config
const result = typeof maybe === 'function' ? await maybe() : undefined
if (typeof result !== 'function') {
  // skip or report this component instead of letting preparePageTemplateConfigs throw
}

const isPageConfigFn = (v: unknown): v is (...args: any[]) => any =>
  typeof v === 'function'

When it happens

Trigger: A registered component in the store has `component.config` truthy, so Gatsby calls `pageRenderer.getPageChunk(...)` then `componentInstance.config()`, but that call resolves to undefined/object/string instead of a function. Common when a page template exports `config` from `gatsby` but re-exports it incorrectly, or when a third-party plugin injects a component with a malformed `config` field.

Common situations: Upgrading a site to a Gatsby version that introduced the page-config API while the page template exports a non-standard `config` value; using DSG/SSR with a template whose `config` export is shadowed by a default export; plugin-authored components registering a `config` field that is not the Gatsby config factory.

Related errors

• Incompatible DSG/SSR executing environment. Function was bui
• Page for "${pathName}" not found
• Page template details for "${page.componentChunkName}" not f
• Loading indicator should never be imported in code that does
• Slice "${sliceName}" was passed props that are not serializa

AI-assisted analysis of gatsbyjs/gatsby@8b06340921 (2026-08-13). Data as JSON: /api/errors/4d861e5b37ddc060. Report an issue: GitHub.