How to iterate a string literal type in typescript

Question

How can I iterate a string literal type in typescript?

For example i define this type

type Name = "Bill Gates" | "Steve Jobs" | "Linus Torvalds"; 

I want to iterate like this

for (let name of Name) {     console.log("Possible name: " + name); } 

Or is this simply not possible in typescript?

Answer 1

Rather than iterating a (union of) string literal types as the OP requested, you can instead define an array literal and if marked as const then the entries' type will be a union of string literal types.

Since typescript 3.4 you can define const assertions on literal expressions to mark that: - no literal types in that expression should be widened (e.g. no going from "hello" to string) - array literals become readonly tuples

For example:

const names = ["Bill Gates", "Steve Jobs", "Linus Torvalds"] as const; type Names = typeof names[number]; 

It can be used at runtime and with types checked, for example:

const companies = {     "Bill Gates" : "Microsoft",     "Steve Jobs" : "Apple",     "Linus Torvalds" : "Linux", } as const;  for(const n of names) {     console.log(n, companies[n]); } const bg : Names = 'Bill Gates'; const ms = companies[bg]; 

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-4.html#const-assertions

https://mariusschulz.com/blog/const-assertions-in-literal-expressions-in-typescript

https://microsoft.github.io/TypeScript-New-Handbook/chapters/types-from-extraction/#indexed-access-types

Answer 2

Since TypeScript is just a compiler, none of the typing information is present at runtime. This means that unfortunately you cannot iterate through a type.

Depending on what you're trying to do it could be possible for you to use enums to store indices of names that you can then retrieve in an array.