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prefer-return-this-type

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

Method chaining is a common pattern in OOP languages and TypeScript provides a special polymorphic this type. If any type other than this is specified as the return type of these chaining methods, TypeScript will fail to cast it when invoking in subclass.

class Animal {
  eat(): Animal {
    console.log("I'm moving!");
    return this;
  }
}

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

const cat = new Cat();
// Error: Property 'meow' does not exist on type 'Animal'.
// because `eat` returns `Animal` and not all animals meow.
cat.eat().meow();

// the error can be fixed by removing the return type of `eat` or use `this` as the return type.
class Animal {
  eat(): this {
    console.log("I'm moving!");
    return this;
  }
}

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

const cat = new Cat();
// no errors. Because `eat` returns `Cat` now
cat.eat().meow();

Attributes​

  • Included in configs
    • ✅ Recommended
    • 🔒 Strict
  • Fixable
    • 🔧 Automated Fixer
    • 🛠 Suggestion Fixer
  • 💭 Requires type information

Rule Details​

Examples of code for this rule:

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

Options​

// .eslintrc.json
{
  "rules": {
    "@typescript-eslint/prefer-return-this-type": "warn"
  }
}

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.