TS 4.4: `exactOptionalPropertyTypes: true` support

[Nicolas Stepien]

TypeScript 4.4's release is around the corner, and I'm testing it right now.
I'm hitting issues with csstype as properties are optional but do not explicitly allow undefined, for example

left?: Property.Left<TLength>;

should be

left?: Property.Left<TLength> | undefined;

https://devblogs.microsoft.com/typescript/announcing-typescript-4-4-rc/

Support for this would be nice.

For reference: adazzle/react-data-grid#2566

[Fredrik Nicol]

My first thought was that maybe it would be expected to fail so you're notified when something can be removed. But I guess you're right. This would be annoying:

let myColor: string | undefined;

if (someCondition) {
  myColor: 'red';
}

const style: CSS.Properties = {
  color: myColor, // Guess this would cause a type error?
}

[Nicolas Stepien]

Yes that's right.

You can also end up with code that looks like this

const style: CSS.Properties = {
  color: records[key], // possibly undefined
  background: [].find(() => false) // possibly undefined
}

[Nicolas Stepien]

It's out!
https://devblogs.microsoft.com/typescript/announcing-typescript-4-4/

[Daniele Orlando]

Waiting for TS 4.4 support too.

[Fredrik Nicol]

Released in 3.0.10