TypeScript / JavaScript - immutable enums

In this short article, we would like to show how to create immutable enums in JavaScript / TypeScript.

During compilation, enums are converted to JavaScript objects that can be changed, which can lead to bugs.

It is necessary to freeze the enum object.

Practical example (JavaScript):

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const CurrencyEnum = {

    'USD': 1,

    'EUR': 2,

    'GBP': 3,

    'CHF': 4,

    'PLN': 5

};

​

Object.freeze(CurrencyEnum);  //  <---------- makes CurrencyEnum as read-only

​

// now CurrencyEnum is read-only

Practical example (TypeScript):

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enum CurrencyEnum {

    USD = 1,

    EUR = 2,

    GBP = 3,

    CHF = 4,

    PLN = 5

};

​

Object.freeze(CurrencyEnum);  //  <---------- makes CurrencyEnum as read-only in pure JavaScript

​

// now CurrencyEnum is read-only from pure JavaScript

Note: Object.freeze() was introduced in ES5 (ECMAScript 2009).