E0221: TypeScript interface fields cannot be initalized

TypeScript interfaces describe the properties of objects, but do not describe default values for those properties. It is a syntax error to initialize a property with = in an interface:

interface Entity {
  x: number = 0;
  y: number = 0;

  tick(): void;
}

class Player implements Entity {
  x: number;
  y: number;

  tick(): void {
    // ...
  }
}

To fix this error, convert the interface into an abstract base class:

abstract class Entity {
  x: number = 0;
  y: number = 0;

  abstract tick(): void;
}

class Player extends Entity {
  tick(): void {
    // ...
  }
}

Alternatively, remove the initializer from the interface, making sure to initialize in implementing classes:

interface Entity {
  x: number;
  y: number;

  tick(): void;
}

class Player implements Entity {
  x: number = 0;
  y: number = 0;

  tick(): void {
    // ...
  }
}

Introduced in quick-lint-js version 2.6.0.

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