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prefer-return-this-type

Enforce that this is used when only this type is returned.

🔒

Extending "plugin:@typescript-eslint/strict" in an ESLint configuration enables this rule.

🔧

Some problems reported by this rule are automatically fixable by the --fix ESLint command line option.

💭

This rule requires type information to run.

Method chaining is a common pattern in OOP languages and TypeScript provides a special polymorphic this type to facilitate it. Class methods that explicitly declare a return type of the class name instead of this make it harder for extending classes to call that method: the returned object will be typed as the base class, not the derived class.

This rule reports when a class method declares a return type of that class name instead of this.

class Animal {
  eat(): Animal {
    //   ~~~~~~
    // Either removing this type annotation or replacing
    // it with `this` would remove the type error below.
    console.log("I'm moving!");
    return this;
  }
}

class Cat extends Animal {
  meow(): Cat {
    console.log('Meow~');
    return this;
  }
}

const cat = new Cat();
cat.eat().meow();
//        ~~~~
// Error: Property 'meow' does not exist on type 'Animal'.
// because `eat` returns `Animal` and not all animals meow.
.eslintrc.cjs
module.exports = {
  "rules": {
    "@typescript-eslint/prefer-return-this-type": "warn"
  }
};

Examples​

class Foo {
  f1(): Foo {
    return this;
  }
  f2 = (): Foo => {
    return this;
  };
  f3(): Foo | undefined {
    return Math.random() > 0.5 ? this : undefined;
  }
}

Options​

This rule is not configurable.

When Not To Use It​

If you don't use method chaining or explicit return values, you can safely turn this rule off.

Resources​