useNamespaceKeyword (since v12.0.0)
Require using the namespace keyword over the module keyword to declare TypeScript namespaces.
TypeScript historically allowed a code organization called namespace. ECMAScript modules are preferred (import / export).
For projects still using namespaces, it’s preferred to use the namespace keyword instead of the module keyword. The module keyword is deprecated to avoid any confusion with the ECMAScript modules which are often called modules.
Note that TypeScript module declarations to describe external APIs (declare module "foo" {}) are still allowed.
Source: https://typescript-eslint.io/rules/prefer-namespace-keyword
See also: https://www.typescriptlang.org/docs/handbook/namespaces-and-modules.html
Examples
Invalid
module Example {}nursery/useNamespaceKeyword.js:1:1 lint/nursery/useNamespaceKeyword FIXABLE ━━━━━━━━━━━━━━━━━━━━━━
⚠ Use the namespace keyword instead of the outdated module keyword.
> 1 │ module Example {}
│ ^^^^^^
2 │
ℹ The module keyword is deprecated to avoid any confusion with the ECMAScript modules which are often called modules.
ℹ Safe fix: Use namespace instead.
1 │ - module·Example·{}
1 │ + namespace·Example·{}
2 2 │
Valid
namespace Example {}declare module "foo" {}