Naming convention for const object keys in ES6

Question

Is there a recommended naming convention for key names within a const object in es6? I haven't been able to find a resource which states if they should be uppercase or lowercase.

const COLOR_CODES = {
  BLUE: 1,
  RED: 1
};

vs

const COLOR_CODES = {
  blue: 1,
  red: 1
};

The examples from this MDN article show both styles, so maybe both are acceptable.

Answer 1

According to Google it would be all caps. Speaking from experience, most of the other programming languages have all caps so I would suggest using that.

Use NAMES_LIKE_THIS for constant values.

Use @const to indicate a constant (non-overwritable) pointer (a variable or property).

Google javascript guide https://google.github.io/styleguide/javascriptguide.xml

Answer 2

NOTE: be aware that the accepted response has a link to an obsolete Google style guide

This is nice (string literals or integer literals):

const PI = 3.14;
const ADDRESS = '10.0.0.1';

but...

const myObject = { key: 'value' };
const userSuppliedNumber = getInputNumber()

Google JavaScript Style Guide says:

Declare all local variables with either const or let. Use const by default, unless a variable needs to be reassigned. The var keyword must not be used.

Every constant is a @const static property or a module-local const declaration, but not all @const static properties and module-local consts are constants. Before choosing constant case, consider whether the field really feels like a deeply immutable constant. For example, if any of that instance's observable state can change, it is almost certainly not a constant. Merely intending to never mutate the object is generally not enough.

JavasScript.info says:

...capital-named constants are only used as aliases for “hard-coded” values.

Answer 3

Google once recommended the following:

const COLOR_CODES = {
  BLUE: 1,
  RED: 1
};

See: https://google.github.io/styleguide/javascriptguide.xml#Constants

• Use NAMES_LIKE_THIS for constant values.
• Use @const to indicate a constant (non-overwritable) pointer (a variable or property).
• Never use the const keyword as it's not supported in Internet Explorer.

However, the updated style guidelines have different recommendations.

Answer 4

Naming conventions are all over the place, I personally still haven't decided on my preference but to add to the discussion this is what Airbnb JavaScript Style Guide says (see the last examples):

// bad
const PRIVATE_VARIABLE = 'should not be unnecessarily uppercased within a file';

// bad
export const THING_TO_BE_CHANGED = 'should obviously not be uppercased';

// bad
export let REASSIGNABLE_VARIABLE = 'do not use let with uppercase variables';

// ---

// allowed but does not supply semantic value
export const apiKey = 'SOMEKEY';

// better in most cases
export const API_KEY = 'SOMEKEY';

// ---

// bad - unnecessarily uppercases key while adding no semantic value
export const MAPPING = {
  KEY: 'value'
};

// good
export const MAPPING = {
  key: 'value'
};