Customizing build to exclude polyfill code

[bradchoate]

• Adds a new "maven_modules" directory with shims for the core-js-pure
  references that are used to polyfill for Array.includes, Array.from,
  Array.find, Array.findIndex, and String.includes.
• Small change to webpack.config.js to search the maven_includes tree
  to resolve references ahead of node_modules.
• Some updates to mavenAnalyticsAdapter.js to allow for a clean test
  suite (some lint errors were present).

ADS-4784

[bradchoate]

This change reduces the Prebid bundle by 28K (uncompressed)!

[bradchoate]

This does not replace the polyfill for Number.isInteger. The entire thing is part of Prebid's util.js module and looks like this:

export function isInteger(value) {
  if (Number.isInteger) {
    return Number.isInteger(value);
  } else {
    return typeof value === 'number' && isFinite(value) && Math.floor(value) === value;
  }
}

So, not a lot of code, compared to the third-party core-js polyfills.

[vipulnaik]

Hi @bradchoate, question: is there any change to the build process for building this for/in Phoenix, as described at https://github.com/themaven-net/tempest-phoenix/blob/master/htdocs/js/prebid/README.md#building-a-new-version?

[bradchoate]

@vipulnaik No, there's no change to the build process. Of course, if we aren't doing a polyfill for these by Phoenix itself, then we will lose support for IE11.

[AritraSengupta]

Should we remove this from webpack as well? (line 36-38)

module.resource && (allowedModules.src.concat(['core-js'])).some(
          name => module.resource.includes(path.resolve('./node_modules/' + name))
        )

Since we do not need to minify core-js anymore?

[AritraSengupta]

The rest looks good. Maybe we can ask Michelle we want to continue supporting IE 11 in Phoenix and then make a call.

[vipulnaik]

@AritraSengupta, @bradchoate that's a good point. Ideally we still want to keep IE 11 support, but we already have a system for loading global polyfills for older browsers, and if needed, we should add more polyfills there: https://github.com/themaven-net/tempest-phoenix/tree/master/htdocs/bootscripts/polyfills That way the extra polyfill code is downloaded only by IE 11 users, and it does not bloat the Prebid bundle.

So the question is: are the polyfills we are eliminating from Prebid already included? It looks like many of them are not. For instance, https://github.com/themaven-net/tempest-phoenix/blob/master/htdocs/bootscripts/polyfills/string/main.js has polyfills for startsWith and endsWith but does not have a polyfill for includes -- which is the one we are getting from core-js. I confirmed that if I load The Street on IE 11, string inclusion is not available for me in the IE 11 console. Similarly, array find and findIndex operations seem unsupported with the polyfills we are currently bringing into Phoenix on IE 11.

This means that, if we want full IE 11 support, parallel work may need to be done to expand our existing polyfills (at https://github.com/themaven-net/tempest-phoenix/tree/master/htdocs/bootscripts/polyfills). @bradchoate do you feel that would be within the scope of this ticket, or should we make a followup ticket for that work? In any case, depending on the level of IE 11 support we want to keep, we may have to block the update of Phoenix with this code until that work is done.

[bradchoate]

@vipulnaik Michelle says our monetization is so low for IE11 that it would be fine if we were to cut support for it. We already had some web component code in Phoenix that breaks under IE11 and haven't bothered to fix it due to lack of priority. Further, there are increasing runtime errors for ads delivered to IE11, where the ad payload itself is not backward compatible with IE11.

[bradchoate]

Should we remove this from webpack as well? (line 36-38)

@AritraSengupta I don't think it's necessary; I was trying to limit changes made to webpack.config.js as much as possible to reduce risk of conflicts with future merges from the upstream repo.

[vipulnaik]

LGTM; can you make sure to pull the updated file into Phoenix, confirm the size reduction, and only close the ticket once the Phoenix side is deployed? Just want to make sure any impact of this is monitored right now rather than affecting somebody later when they need to pull an updated Prebid into Phoenix.

Thanks!

[bradchoate]

Merged to stable, stable-next branches manually.