What does the following conditional type evaluate to? type IsString = T extends string ? true : false; type A = IsString; type B = IsString;

Question

TypeScript Associate — Hard

What does the following conditional type evaluate to? type IsString = T extends string ? true : false; type A = IsString; type B = IsString;

Accepted Answer

The conditional type IsString evaluates to true if T extends string, otherwise false. In this case, both A and B are assigned the value of IsString, resulting in A being true and B being a boolean distributed over the union: true | false.