TypeError when running component tests with Next.js 16 and Webpack

[KenTandrian]

Current behavior

Cypress fails to load the configuration file and throws the following error:

TypeError: webpackModule.init is not a function
    at sourceNextWebpack (/Users/me/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/helpers/nextHandler.js:308:19)
    at sourceNextWebpackDeps (/Users/me/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/helpers/nextHandler.js:268:21)
    at nextHandler (/Users/me/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/helpers/nextHandler.js:18:74)
    at async getPreset (/Users/me/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/devServer.js:60:20)
    at async devServer.create (/Users/me/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/devServer.js:79:61)
    at async /Users/me/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/devServer.js:22:24

Desired behavior

Cypress should successfully load the configuration file and run the component tests without errors.

Test code to reproduce

https://github.com/KenTandrian/cypress-nextjs-16-webpack

Reproduction Steps:

1. Create a Next.js project (version 16.0.0).
2. Install Cypress (version 15.5.0) with component testing support.
3. Configure Cypress to use the Next.js framework and webpack bundler in cypress.config.ts.
4. Attempt to run component tests using the command yarn cypress run --component.

Cypress Version

15.5.0

Debug Logs

N/A -- it fails before running the test.

Other

The issue started occurring after upgrading to Next.js version 16. This suggests a potential incompatibility or breaking change introduced in Next.js 16.

I believe the error stems from the Cypress code still calling webpackModule.init here:

cypress/npm/webpack-dev-server/src/helpers/nextHandler.ts

Line 360 in 2279857

webpackModule.init(webpack5)

This function no longer exists in the newer node_modules/next/dist/compiled/webpack/webpack.js file in Next.js 16.

Previous:
https://github.com/vercel/next.js/blob/de19200deb33869fc691b43e68aef76493d79fa1/packages/next/src/compiled/webpack/webpack.js#L5

Now:
https://github.com/vercel/next.js/blob/d27f18f390ce2ac5728fb902a004381d876e85bd/packages/next/src/compiled/webpack/webpack.js#L5

[chinmaykunkikar]

Thank you for reporting this. I am facing the same issue on my next v16 migration branch. I cannot merge it unless the tests start running again.

Cypress Version: 15.5.0

Next.js version: 16.0.1

> cypress run --component --browser chrome --port 3400


DevTools listening on ws://127.0.0.1:64501/devtools/browser/44ee0144-df42-4ee4-bd78-b8d8564f7822
Your configFile threw an error from: cypress.config.js

We stopped running your tests because your config file crashed.

TypeError: webpackModule.init is not a function
    at sourceNextWebpack (/Users/chinmay/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/helpers/nextHandler.js:308:19)
    at sourceNextWebpackDeps (/Users/chinmay/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/helpers/nextHandler.js:268:21)
    at nextHandler (/Users/chinmay/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/helpers/nextHandler.js:18:74)
    at async getPreset (/Users/chinmay/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/devServer.js:60:20)
    at async devServer.create (/Users/chinmay/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/devServer.js:79:61)
    at async /Users/chinmay/Library/Caches/Cypress/15.5.0/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-dev-server/dist/devServer.js:22:24

[MikeMcC399]

Next.js 16 was announced on Oct 21, 2025.

https://docs.cypress.io/app/component-testing/get-started#Supported-Frameworks shows Next.js 14-15 as being supported for Cypress Component Testing, so this issue would need to be worked on as an enhancement request.