Migrate to ES2020 Compile Target

[witemple-msft]

We advanced our compiler target to ES2017 when support for Internet Explorer was dropped. This issue is to track the next upgrade of our compiler target to ES2020 now that Node.js 14 is our minimum node target

Our extended support for Node.js 12 ended on November 1, 2022. At that point, we ought to be able to:

1. Elevate the default compiler target to ”es2020” in /tsconfig.json.
2. Safely use “es2020” library declarations without worrying about polyfills.

This comes with benefits. We would no longer have to downlevel the following syntaxes (most are polyfilled using tslib helpers when targeting ES2017):

• async generators (async function*() {})
• async iteration (for await (const x of iterable) {})
• object rest properties (const { foo, bar, ...rest } = someValue;)
• object spread (const someValue = { foo, bar, ...rest };)
• nullish coalescing (??)
• optional chaining (.?)

We would also be able to use private identifiers.

And that we could use the following runtime environment features:

• Promise.prototype.finally
• Array.prototype.flat & Array.prototype.flatMap
• String.prototype.trim{Left,Right,Start,End}

CC @xirzec @bterlson

[xirzec]

Sounds like a nice step forward to me. 👍

[jeremymeng]

It appears that we are still on ES2017 in /tsconfig.json. maybe when we move to Node 16 we can migrate to 2021 or even 2022. We may be blocked by esm not supporting optional chaining/nullish coalecsing but there's a workaround standard-things/esm#918

[github-actions]

Hi @witemple-msft, we deeply appreciate your input into this project. Regrettably, this issue has remained inactive for over 2 years, leading us to the decision to close it. We've implemented this policy to maintain the relevance of our issue queue and facilitate easier navigation for new contributors. If you still believe this topic requires attention, please feel free to create a new issue, referencing this one. Thank you for your understanding and ongoing support.