Transform string literal type into union of characters in TypeScript

Today we discuss StringToUnion

Type transformations are useful for different types of tasks.

We already discussed:

• Tuple to Object in Making object out of tuple
• Tuple to Union in Making union out of tuple

Let's go 🚀

Iteration over a string

Let's start from the first character:

We cannot extract it using indices as we get string. Instead let's apply Type inference in conditional types:

Putting characters into a union

Next step is to put other characters into a union.

As we already can get first character, let's apply it recursively:

On the final step where we have an empty string, it converts to never

If we deal with a union type, never is the type when we have no elements in it. But if we put any element in it, never will be removed from it:

That's it 💫

Don't forget to check the final solution on Playground – https://tsplay.dev/N7bXqw

Have a wonderful weekend ☀️