String enum like type in typescript [duplicate]

Question

Edit: TypeScript now has string enums.

I am looking for a string enum that can be iterated.

What I tried so far:

String union types:

type t = "p1" | "p2" | "p3"

Problem: Can't be iterated

Enum:

enum t { p1, p2, p3 }

Problem: can't have string enum

Object:

const t = {p1: "p1", p2: "p2", p3: "p3"}

Problem: can't strongly type a variable that should be "p1", "p2", or "p3"

I could use an object and string union types or an enum and a map but I end up repeating myself a lot. What is the proper way to get a string enum that you can iterate in typescript?

This is javascript, it has strings, numbers, objects as types. It's not a statically typed language either. So you may want to rethink the problem you're trying to solve here and whether strong typing is what you need. — Callum Linington
– Callum Linington, Commented Jun 8, 2016 at 17:48
@CallumLinington I tagged it typescript too. Typescript is a typed superset of javascript — michaelmesser
– michaelmesser, Commented Jun 8, 2016 at 17:49
You're running into a limitation of Javascript, which doesn't have a representation for typing, or enums. See the link that David Sherret posted for how to represent in Javascript. — Alex Ruiz
– Alex Ruiz, Commented Jun 8, 2016 at 17:55

p.s.w.g · Accepted Answer · 2016-06-08 18:18:03Z

1

I'm not sure why you need the value to be a string. Note that you can get the enum value from its name using t.p1 or t["p1"], and you can get it's name from its enum value using t[0].

For example:

enum t { p1, p2, p3 }

function foo(x : t) {
    console.log(`value: ${x}, name: "${t[x]}"`);
}
foo(t.p1);      // value: 0, name: "p1"
foo(t["p1"]);   // value: 0, name: "p1"

But if you really need to accept string values, you could always do this (yes, this would get pretty redundant after a while):

function foo(x : t | "p1" | "p2" | "p3") {
    if (typeof x == "string") x = t[x];
    console.log(`value: ${x}, name:"${t[x]}"`);
}

foo("p1");      // value: 0, name: "p1"

edited Jun 8, 2016 at 18:18

answered Jun 8, 2016 at 18:08

p.s.w.g

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2 Comments

michaelmesser Over a year ago

Can you iterate over an enum?

p.s.w.g Over a year ago

@2426021684 Sure, see this answer.

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