implement enum as immutable class in modern javascript (es2015)

Question

I need some help. I want to implement Enum with modern javascript. I want it to be immutable and think it will looks something like that:

class AlphabetEnum{
  static get A(){
     return 'a';
  },
  static get B(){
     return 'b';
  }
 ...
}

However, it's a bit annoying to write all this getters. So I'm curious - is there a chance to optimize this with compute method names and maybe some other es2015 features.

In result I dream to have something like that:

let alph = [a, b, c, ..., z];
class AlphabetEnum{
      static get [some__clever_way_to_resolve_names_from_<alph>](){
         return some_clever_way_to_understand_what's_called();
      },
    }

Bergi · Accepted Answer · 2015-11-30 14:43:59Z

6

A class makes just no sense. You don't a want a function with static getters. You just want an immutable object - and that's easy:

const AlphabetEnum = Object.freeze({
    A: "a",
    B: "b",
    …
});

Of course you can also dynamically create that if listing all properties is too cumbersome:

const AlphabetEnum = {};
for (let i=0; i<26; i++)
    AlphabetEnum[String.fromCharCode(65+i)] = String.fromCharCode(97+i);
Object.freeze(AlphabetEnum);

answered Nov 30, 2015 at 14:43

Bergi

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Comments

Felix Kling · Accepted Answer · 2015-11-30 14:41:05Z

3

You'd do it the same way is in ES5, with Object.defineProperty:

class AlphabetEnum {}

['a', 'b', 'c', ..., 'z'].forEach(letter => {
  Object.defineProperty(AlphabetEnum, letter.toUpperCase(), {
    get: () => letter,
    configurable: true, // remove this line if not needed / wanted
  });
});

However, using a class just for static properties is an anti-pattern IMO. In that case you can as well use a plain object:

var AlphabetEnum = {};

edited Nov 30, 2015 at 14:41

answered Nov 30, 2015 at 14:37

Felix Kling

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8 Comments

Arg0n Over a year ago

You may want to remove the comma after configurable: true, otherwise nice answer :).

Felix Kling Over a year ago

@Arg0n: Why should I do that?

Cerbrus Over a year ago

Because that's prettier! (Which is totally a fact, not an opinion) v++

Arg0n Over a year ago

@FelixKling Hmm, i just think it looks like an object and that you will get syntax error with the comma after the last property? But since you say you don't need to i guess you're right.

Felix Kling Over a year ago

@Arg0n: A trailing comma in an object literal is not a syntax error :)

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