JVerstry JVerstry - 13 days ago 7
Javascript Question

Declaring static constants in ES6 classes?

I want to implement constants in a

class
, because that's where it makes sense to locate them in the code.

So far, I have been implementing the following workaround with static methods:

class MyClass {
static constant1() { return 33; }
static constant2() { return 2; }
// ...
}


I know there is a possibility to fiddle with prototypes, but many recommend against this.

Is there a better way to implement constants in ES6 classes?

Answer

Here's a few things you could do:

Export a const from the module. Depending on your use case, you could just:

export const constant1 = 33;

And import that from the module where necessary. Or, building on your static method idea, you could declare a static get accessor:

const constant1 = 33,
      constant2 = 2;
class Example {

  static get constant1() {
    return constant1;
  }

  static get constant2() {
    return constant2;
  }
}

That way, you won't need parenthesis:

const one = Example.constant1;

Babel REPL Example

Then, as you say, since a class is just syntactic sugar for a function you can just add a non-writable property like so:

class Example {
}
Object.defineProperty(Example, 'constant1', {
    value: 33,
    writable : false,
    enumerable : true,
    configurable : false
});
Example.constant1; // 33
Example.constant1 = 15; // TypeError

It may be nice if we could just do something like:

class Example {
    static const constant1 = 33;
}

But unfortunately this class property syntax is only in an ES7 proposal, and even then it won't allow for adding const to the property.

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