Typescript Numeric Literal Types How To X + Y (Addition)

Have you ever wondered how to add 2 numeric literal types?

now you know

type CreateArrayWithLengthX<
LENGTH extends number,
ACC extends unknown[] = [],
> = ACC['length'] extends LENGTH
? ACC
: CreateArrayWithLengthX<LENGTH, [...ACC,1]>
type AddTwoNumber<T extends number, U extends number> = [...CreateArrayWithLengthX<T>,...CreateArrayWithLengthX<U>]['length']type A = AddTwoNumber<999,999> //1998

playground

limitation: the number cannot exceed 999 because the max depth of TS recursion is only 1000, only work with positive integer

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