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noMisleadingInstantiator (since v1.3.0)

Diagnostic Category: lint/suspicious/noMisleadingInstantiator

Sources:

Enforce proper usage of new and constructor.

In JavaScript, classes utilize the constructor method to initialize a new instance. On the other hand, TypeScript interfaces can describe a class type with a new() method signature, though this pattern is not commonly seen in real-world code. Developers, especially those new to JavaScript or TypeScript, might occasionally confuse the use of constructor with new. This rule triggers warnings in the following scenarios:

  • When a class has a method named new.
  • When an interface defines a method named constructor or new that returns the interface type.
  • When a type alias has a constructor method.

You should not use this rule if you intentionally want a class with a new method, and you’re confident nobody working in your code will mistake it with an constructor.

Examples

Section titled Examples

Invalid

Section titled Invalid
interface I {
  new (): I;
  constructor(): void;
}
suspicious/noMisleadingInstantiator.js:2:3 lint/suspicious/noMisleadingInstantiator ━━━━━━━━━━━━━━━━

  ✖ Don't use the new method in interfaces.
  
    1 │ interface I {
  > 2 │   new (): I;
      │   ^^^^^^^^^^
    3 │   constructor(): void;
    4 │ }
  
  ℹ new in an interface suggests it's instantiable, which is incorrect. The returned type should different from the constructor's type.
  

class C {
  new(): C;
}
suspicious/noMisleadingInstantiator.js:2:3 lint/suspicious/noMisleadingInstantiator ━━━━━━━━━━━━━━━━

  ✖ Don't use the new method in classes.
  
    1 │ class C {
  > 2 │   new(): C;
      │   ^^^^^^^^^
    3 │ }
    4 │ 
  
  ℹ new is typically used to instantiate objects. In classes, its usage can be misleading.

Valid

Section titled Valid
declare class C {
  constructor();
}


interface I {
  new (): C;
}
Section titled Related links