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prefer-return-this-type

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

🔒

Extending "plugin:@typescript-eslint/strict-type-checked" 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": "error"
  }
};

Try this rule in the playground ↗

Examples​

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

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.

Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. See Troubleshooting > Linting with Type Information > Performance if you experience performance degredations after enabling type checked rules.

Resources​