Why is this an issue?

Initially, TypeScript defined "internal modules" and "external modules":

• Internal modules: The module keyword was introduced in TypeScript to define internal modules. Internal modules were used to group classes, interfaces, and functions into logical units.
• External modules refer to JavaScript modules, introduced in ECMAScript 2015. In TypeScript, just as in JavaScript (after ECMAScript 2015), any file containing a top-level import or export is considered a module.

However, in order to avoid confusion with similarly named terms, module was deprecated in favor of the namespace keyword, and "external modules" became simply "modules", as to align with ECMAScript 2015’s terminology.

Now that namespace is available, the use of module is deprecated because it does the same thing, and its use could confuse maintainers unaware of the history of the language. Therefore, the use of module is discouraged in TypeScript code.

module myMod {  // Noncompliant
  // ...
}

Anywhere the module keyword was used when declaring an internal module, the namespace keyword should be used instead.

namespace myMod {
  // ...
}

Resources

Documentation

• TypeScript Documentation - Namespaces
• TypeScript Documentation - Modules
• ECMAScript - ECMAScript 2015