Allow Custom webVitals Endpoint in performance-relayer.ts

[simonireilly]

Feature request

This feature request is to allow for a custom URL in the vitalsUrl in performance-relayer.ts

Is your feature request related to a problem? Please describe.

The use case for this is to aggregate the webVitals from NextJS in any third-party tool using the efficient code path already present in the NextJS framework.

Describe the solution you'd like

An ideal solution would be to allow the URL to be set in the next.config.js so that it can be statically configured before the build.

module.exports = {
  vitalsUrl: '/api/v1/vitals'
}

Describe alternatives you've considered

Alternative 1

You can alternatively just engage analytics and monkey-patch through webpack:

module.exports = (phase, { defaultConfig }) => {
  defaultConfig.analyticsId = 'custom-id-for-application'

  defaultConfig.webpack = (config, options) => {
    config.module.rules.push(      {
      test: /performance-relayer\.js$/,
      loader: 'string-replace-loader',
      options: {
        search: 'https://vitals.vercel-analytics.com/v1/vitals',
        replace: '/api/v1/vitals',
        flags: 'g'
      }
    })

    return config
  }

  return defaultConfig
}

Alternative 2

You can follow the steps in https://nextjs.org/docs/advanced-features/measuring-performance to set up a custom implementation. This seems suboptimal given the best practices baked into performance-relayer.ts

Additional context

N/A

Thanks, I would of course understand if this is to remain a private API to allow for feature development.

[Timer]

We intentionally designed this in such a way that it is code eliminated when unused. Exposing this as a public API would prevent us from iterating on it in the future, as we'd need to keep semver-compliance.

Any custom analytics reporting should be introduced via reportWebVitals, which is semver stable.

There is nothing we do that you cannot do with the above method. Plus, you'll be able to send things in the exact shape you want (or ignore TTFB, etc)!

[simonireilly]

@Timer that makes a great deal of sense, thanks for your response 👍

[balazsorban44]

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