next.js/test/production/disable-fallback-polyfills/index.test.ts

import { createNext } from 'e2e-utils'
import { NextInstance } from 'e2e-utils'

// TODO: Implement experimental.fallbackNodePolyfills
;(process.env.IS_TURBOPACK_TEST ? describe.skip : describe)(
  'Disable fallback polyfills',
  () => {
    let next: NextInstance

    function getFirstLoadSize(output: string) {
      const firstLoadRe =
        /○ \/.*? (?<size>\d.*?) [^\d]{2} (?<firstLoad>\d.*?) [^\d]{2}/
      return Number(output.match(firstLoadRe).groups.firstLoad)
    }

    beforeAll(async () => {
      next = await createNext({
        files: {
          'pages/index.js': `
          import { useEffect } from 'react'
          import crypto from 'crypto'

          export default function Page() {
            useEffect(() => {
              crypto;
            }, [])
            return <p>hello world</p>
          } 
        `,
        },
        dependencies: {
          axios: '0.27.2',
        },
      })
      await next.stop()
    })
    afterAll(() => next.destroy())

    it('Fallback polyfills added by default', async () => {
      expect(getFirstLoadSize(next.cliOutput)).not.toBeLessThan(200)
    })

    it('Reduced bundle size when polyfills are disabled', async () => {
      await next.patchFile(
        'next.config.js',
        `module.exports = {
        experimental: {
          fallbackNodePolyfills: false
        }
      }`
      )
      await next.start()
      await next.stop()

      expect(getFirstLoadSize(next.cliOutput)).toBeLessThan(200)
    })

    it('Pass build without error if non-polyfilled module is unreachable', async () => {
      // `axios` uses `Buffer`, but it should be unreachable in the browser.
      // https://github.com/axios/axios/blob/649d739288c8e2c55829ac60e2345a0f3439c730/lib/helpers/toFormData.js#L138
      await next.patchFile(
        'pages/index.js',
        `import axios from 'axios'
       import { useEffect } from 'react'

       export default function Home() {
         useEffect(() => {
           axios.get('/api')
         }, [])

         return "hello world"
       }`
      )

      await expect(next.start()).not.toReject()
    })
  }
)