Declaring static constants in ES6 classes?

Question

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 1

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.

Answer 2

class Whatever {     static get MyConst() { return 10; } }  let a = Whatever.MyConst; 

Seems to work for me.