Load the main JS bundle in production with async

[arunoda]

Fixes #1436

With this, we don't need to wait for the JS bundle and page can render directly.
This will lead to better page load performance.

[ptomasroos]

Great improvments @arunoda

[timneutkens]

Niiiiice 😍 ❤️

[timneutkens]

is not tight with a chunk.

is not tied to a chunk is more correct here right?

[arunoda]

Thanks.

[timneutkens]

pulgin => plugin

[matthewmueller]

should we also defer this bundle?

[arunoda]

should we also defer this bundle?
No. Defer and Async are different stuff. We might use that for backward compatibility.
But since we only focus on IE9+, this is fine.

[tomevans18]

I feel like this topic has been done to death but I wanted to comment and make sure I'm on the right lines and nothing has been missed.

After trying to improve the performance of a site I'm working on I came across this PR.
On review of Chrome's performance profiler, I noticed that the main.js file is taking a long time to evaluate (1.6 seconds in my case) and this seems to be slowing down the sites first meaningful paint.

My initial thought is deferring this file (along with all other JS) as it is not needed initially due to SSR.

What are your thoughts? Maybe all JS should be loaded after the DOM on initial load.
Is this achievable?

[timneutkens]

The long evaluation is probably fixed by #4639 as main.js used to serve as main bundle + commons but is now split.

In general, it makes not much sense to comment on a 1-year-old pull request to ask for help.

[tomevans18]

@timneutkens thanks for the info regarding #4639, I will keep an eye on that PR.

Apologies, I understood it was an old PR hence cavitating the comment with "I feel like this topic has been done to death". I could see that there were several comments on an issue (#1436) and this PR was to resolve it, with no future issues or PRs referencing this problem... hence the comment above.