prefer-module-scope-constants.md

Prefer that screaming snake case variables always be defined using const, and always appear at module scope. (prefer-module-scope-constants)

We use screaming snake case variables to denote truly constant data used for other operations in the file. However, we don’t use this naming convention for all constants — only those that are only ever generated once, at module definition. This rule restricts this naming convention to be used only for these types of constants.

Rule details

Two different errors are flagged by the rule: screaming snake case bindings that are not defined using const, and those that do not appear at module scope.

The following patterns are considered warnings:

// these kinds of values should never change
let MY_VALUE = true;

function myFunction() {
  // this is just a regular `const`, use camelcase instead.
  const OTHER_VALUE = false;
}

if (condition()) {
  // same here, just a regular `const`.
  const FINAL_VALUE = true;
}

The following patterns are not warnings:

const MY_VALUE = true;

function myFunction() {
  const otherValue = false;
}