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loevborg • yesterday at 7:12 PM • 2 replies • view on HN

FWIW, Typescript is using Strategy 2: https://www.typescriptlang.org/play/?#code/GYVwdgxgLglg9mABM...

I'm a bit confused by the fact that the array starts out typed as `any[]` (e.g. if you hover over the declaration) but then, later on, the type gets refined to `(string | number)[]`. IMO it would be nicer if the declaration already showed the inferred type on hover.

Replies

sheept • yesterday at 8:31 PM

I agree, it's always been unsettling to see any[] on hover, even though it gets typed in the end.

I think one reason might be to allow the type to be refined differently in different code paths. For example:

    function x () {
        let arr = []
        if (Math.random() < 0.5) {
            arr.push(0)
            return arr
        } else {
            arr.push('0')
            return arr
        }
    }
In each branch, arr is typed as number[] and string[], respectively, and x's return type is number[] | string[]. If it decided to retroactively infer the type of arr at declaration, then I'd imagine x's return type would be the less specific (number | string)[].
bastawhiz • yesterday at 7:16 PM

It depends on your tsconfig. An empty array could be typed as never[], forcing you to annotate it.

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