noMisleadingInstantiator

Diagnostic Category: lint/suspicious/noMisleadingInstantiator

TypeScript and TSX

Since: v1.3.0

Sources:

Same as: @typescript-eslint/no-misused-new

Description

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

Invalid

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

code-block.ts: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;
}

code-block.ts: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

declare class C {
  constructor();
}

interface I {
  new (): C;
}

How to configure

{
  "linter": {
    "rules": {
      "suspicious": {
        "noMisleadingInstantiator": "error"
      }
    }
  }
}