Rule proposal: `prefer-top-level-await`

Prefer top-level await instead of async IIFE or a top-level function call to an async function.

https://github.com/tc39/proposal-top-level-await

Top-level await is supported in Node.js since Node.js v14.3.0. So we cannot yet add it to the recommended preset, but we can add a TODO comment.

The async IIFE pattern is quite popular in command-line apps: https://github.com/sindresorhus/is-online-cli/blob/fb03be268bdec08e264dad31c5e7a110579d02f6/cli.js#L26-L33

Fail

(async () => {
	await getUnicorns();
})();

function main() {
	await getUnicorns();
}

main();

Pass

await getUnicorns();

[fisker]

Summary,

1. Top level Async IIFE

(async function () {})();

(async () => {})();

1. Top level call

fn(); // `fn` is an async function

1. Top level promise

anything.{then,catch,finally}();

include

(async () => {}).catch();

Enough?

[fisker]

Stage 4 now https://github.com/tc39/proposals/commit/99fa42a0863b1915eccead5bd2939ed5f468caab