[BUGFIX beta] fix for TS 5.1 nightly narrowing change #20441
Merged
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The type here was
any
and sort of narrowing before; now it checks explicitly whether it isstring
. TS 5.1 seems to have a change (maybe a regression?) in how it narrows between the two branches, but previous versions simply fell back toany
anyway rather than narrowing to the inferred types. This unblocks us for TS 5.1, but we should also rewrite this function handler entirely: if it were just two functions instead of using variadic function args, it would dramatically simplify all of this implementation (and almost certainly perform better, too!).