What does the following TypeScript produce? type Flatten = T extends Array ? U : T; type A = Flatten; type B = Flatten;

Question

TypeScript Associate — Hard

What does the following TypeScript produce? type Flatten = T extends Array ? U : T; type A = Flatten; type B = Flatten;

Accepted Answer

The TypeScript code defines a type Flatten that checks if T is an array, then assigns U; otherwise, it assigns T. A and B are both assigned the type Flatten, resulting in A being a string and B being a number.