vitest-dev/vitest · error · TypeError

The " " browser provider does not provide a…

Error message

The "${name}" browser provider does not provide a "providerFactory" function. Received ${typeof options.provider.providerFactory}.

What it means

A TypeError thrown when the resolved provider object exists but its providerFactory field is not a function. The factory is what Vitest calls as providerFactory(project) to build the live provider instance; a missing/non-function factory means the provider object is malformed.

Solutions

If shipping a custom provider, expose providerFactory: (project) => BrowserProviderInstance as a method on the provider definition.
Upgrade or downgrade the provider package to the version compatible with your installed @vitest/browser (check the peer range).
Audit your provider object dump (console.log(options.provider)) to confirm the expected function exists at the right key.

Example fix

// before: custom provider missing the factory
const myProvider = { name: 'mine', supportedBrowser: ['chromium'] }
// after
const myProvider = {
  name: 'mine',
  supportedBrowser: ['chromium'],
  providerFactory: (project) => new MyProviderInstance(project),
}

Defensive patterns

Strategy: type-guard

Validate before calling

function assertProviderFactory(p) {
  if (typeof p?.providerFactory !== 'function') {
    throw new TypeError(`Provider "${p?.name}" is missing providerFactory(project).`)
  }
}

Type guard

function hasProviderFactory(p): p is { providerFactory: (project: unknown) => unknown } {
  return !!p && typeof p.providerFactory === 'function'
}

Prevention

When writing a custom provider, type it against the BrowserProvider interface so the factory is enforced at compile time.
Pin provider package versions to the compatible range; providerFactory was introduced in a specific major.

When it happens

Trigger: options.provider passes the null check and the supportedBrowser check, but typeof options.provider.providerFactory !== 'function' — e.g. it is undefined, a string, or an object.

Common situations: A hand-rolled custom provider that omits the providerFactory method; a provider package whose public surface changed across versions (breaking change); partial mock of a provider in a plugin.

Related errors

AI-assisted analysis of vitest-dev/vitest@1fa9837ec2 (2026-08-11). Data as JSON: /api/errors/69a9d457293db0c3. Report an issue: GitHub.

Appendix: source

Thrown at packages/browser/src/node/utils.ts:91

  const name = project.name ? `[${project.name}] ` : ''
  if (!browser) {
    throw new Error(
      `${name}Browser name is required. Please, set \`test.browser.instances[].browser\` option manually.`,
    )
  }
  if (options.provider == null) {
    throw new Error(`Browser Mode requires the "provider" to always be specified.`)
  }
  const supportedBrowsers = options.provider.supportedBrowser || []
  if (supportedBrowsers.length && !supportedBrowsers.includes(browser)) {
    throw new Error(
      `${name}Browser "${browser}" is not supported by the browser provider "${
        options.provider.name
      }". Supported browsers: ${supportedBrowsers.join(', ')}.`,
    )
  }
  if (typeof options.provider.providerFactory !== 'function') {
    throw new TypeError(`The "${name}" browser provider does not provide a "providerFactory" function. Received ${typeof options.provider.providerFactory}.`)
  }
  return options.provider.providerFactory(project)
}

export function slash(path: string): string {
  return path.replace(/\\/g, '/').replace(/\/+/g, '/')
}

export function assertBrowserFileAccess(project: TestProject, path: string): void {
  const normalized = slash(path)
  if (
    !isFileLoadingAllowed(project.vite.config, normalized)
    && !isFileLoadingAllowed(project.vitest.vite.config, normalized)
  ) {
    throw new Error(
      `Access denied to "${path}". See Vite config documentation for "server.fs": https://vitejs.dev/config/server-options.html#server-fs-strict.`,
    )
  }

View on GitHub (pinned to 1fa9837ec2)