Why is this an issue?

JavaScript and TypeScript classes may define a constructor method that is executed when a new instance is created. TypeScript allows interfaces that describe a static class object to define a new() method. Using these terms to name methods in other contexts can lead to confusion and make the code unclear and harder to understand.

This rule reports when:

A class defines a method named new. The new keyword is used to create new instances of the class. If a method with the same name is defined, it can be unclear whether the method is intended to create new instances or perform some other action.
An interface defines a method named constructor. The constructor method is used to define the constructor function for a class that implements the interface. If a method with the same name is defined in the interface, it can be unclear whether the method is intended to define the constructor function or perform some other action.

interface I {
  constructor(): void; // Noncompliant
  new(): I;
}

declare class C {
  constructor();
  new(): C; // Noncompliant
}

Do not define methods named constructor on TypeScript interfaces. Similarly, avoid defining class methods called new.

interface I {
  new(): I;
}

declare class C {
  constructor();
}

Why is this an issue?

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