I wish that TS had better type narrowing for the JS standard library, though there's a lot of constraints and design limitations that make it impractical. I ran into a similar issue with the some() method on Array not narrowing types a while back [1]; that issue links to the same sort of issue with filter(), as well as issues where the TS team has discussed what they can and can't do in control flow analysis.
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I wish that TS had better type narrowing for the JS standard library, though there's a lot of constraints and design limitations that make it impractical. I ran into a similar issue with the some() method on Array not narrowing types a while back [1]; that issue links to the same sort of issue with filter(), as well as issues where the TS team has discussed what they can and can't do in control flow analysis.
[1] https://github.com/microsoft/TypeScript/issues/40844
you can improve it a bit with the library ts-reset
https://github.com/total-typescript/ts-reset
And also can declare your own wrappers to at least achieve it for your own codebase.