he/him 
JS Type Checker Wish List: Regex validated strings
type HexColor = /#[0-9a-f]+/i;
const color: HexColor = '#eee'; // fine
const color: HexColor = 'red'; // error!
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This is what
@flowtype opaque types are for. Opaque types are super flexible as they can support arbitrary constraints on any value. Also see dependent type systems.
Unclear how that would cover this use case? Imagine you had some CSS-in-JS API where you have your CSS properties typed. How would you define the `color` property without just using `string`?
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You could change your CSS-in-JS library’s API a bit and use opaque types to be fully safe. E.g. instead of colour being a string it has to be an opaque type RGB that can only be created using an rgb function that takes three numbers. + other cases.
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I don't want runtime validation of the types, and the CIJ library needs all style values to be static.
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Oh, I see how this would be better than an opaque type now!
With opaque types you’d need a constructor function like color(string) which would throw at runtime instead of reporting a static error. Presumably you already have that for your CSS-in-JS framework though.Thanks. Twitter will use this to make your timeline better. UndoUndo
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