The TypeScript type system offers a basic support for composite types:

Duplicating types when defining a union or interaction type makes the code less readable. Moreover duplicated types might be a simple mistake and another type should be used instead.

Noncompliant Code Example

function padLeft(value: string, padding: string | number | string) { // Noncompliant; 'string' type is used twice in a union type declaration
  // ...
}

function extend(p : Person) : Person & Person & Loggable { // Noncompliant; 'Person' is used twice
 // ...
}

Compliant Solution

function padLeft(value: string, padding: string | number | boolean) {
  // ...
}

function extend(p : Person) : Person & Loggable {
  // ...
}