Check if string is in ENUM typescript

Question

I have some emun like this

export enum Languages {
  nl = 1,
  fr = 2,
  en = 3,
  de = 4
}

and some const language ='de'; I only need to check does enum constraint const language, i know with array I can do includes but how to check ENUM?

Also I know i can check like this

if (type in Languages) {
}

but this work is it number and not string

Answer 1

You can use Object.keys() in order to access the enum keys followed by a simple Array.prototype.includes():

enum Languages {
  nl = 1,
  fr = 2,
  en = 3,
  de = 4,
}

const language = "de";

console.log(Object.keys(Languages).includes(language)); //true

TypeScript playground

This works because an Enum, when transpiled into JavaScript, becomes nothing more than a simple object:

var Languages;
(function(Languages) {
  Languages[(Languages["nl"] = 1)] = "nl";
  Languages[(Languages["fr"] = 2)] = "fr";
  Languages[(Languages["en"] = 3)] = "en";
  Languages[(Languages["de"] = 4)] = "de";
})(Languages || (Languages = {}));

console.log(Languages);

.as-console-wrapper {
  min-height: 100%;
}