Narrow String#toLowerCase/toUpperCase return types via Lowercase/Uppercase#3711
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ljharb wants to merge 1 commit intomicrosoft:mainfrom
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Narrow String#toLowerCase/toUpperCase return types via Lowercase/Uppercase#3711ljharb wants to merge 1 commit intomicrosoft:mainfrom
ljharb wants to merge 1 commit intomicrosoft:mainfrom
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…rcase Make String.prototype.toLowerCase and toUpperCase preserve string-literal types in their return type, by typing them as `<T extends string>(this: T): Lowercase<T>` and `Uppercase<T>` respectively. For non-literal `string` receivers, `Lowercase<string>` resolves to `string`, preserving existing behavior. For literal receivers (e.g. `"FOO".toLowerCase()`), the result narrows to the corresponding literal (`"foo"`).
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Make String.prototype.toLowerCase and toUpperCase preserve string-literal types in their return type, by typing them as
<T extends string>(this: T): Lowercase<T>andUppercase<T>respectively.For non-literal
stringreceivers,Lowercase<string>resolves tostring, preserving existing behavior. For literal receivers (e.g."FOO".toLowerCase()), the result narrows to the corresponding literal ("foo").