Allow return type annotations on setters

[eligrey]

Setters can return values, so TypeScript should support declaring return types on setters.

🔎 Search Terms

setter return type

🕗 Version & Regression Information

This is the behavior in every version I tried, and I reviewed the FAQ for relevant entries

⏯ Playground Link

• Without return type: https://www.typescriptlang.org/play/?#code/MYewdgzgLgBAZiEMC8MDeAoGMIFNYBGAhgE4AUA+gJTpbYwn4CuJYMA5I1C2wG5EAbJrnYBuOgF8ME8aEiw8UKLhIQAwkTAAlZqwBqg4RBQwA8gQBWuYFAB0Ac3ymA7mAAKJEAAcVUAJ4AIrgQwCQAll5QIOQIIAA0HMQk7FS2imQ0yFkcXDww-EIisuAQIAK4tgIg9mQABorKqjDAmgAkaA0q6po63PqGwQD8HOwwAFwwAETsUJMSDLp8AxC1VKJAA
• With return type: https://www.typescriptlang.org/play/?#code/MYewdgzgLgBAZiEMC8MDeAoGMIFNYBGAhgE4AUA+gJQBcOUJAlmAObpbYwn4CuJYMAOTcofAQDciAGx65BAbg4BfDEsWhIsPFCi4SEAMJEwAJV78AatNkQUMAPIEAVrmBQAdC3z2A7mAAKJCAADnpQAJ4AIrgQwEzBUCDkCCAANELEJIJU7tpkVCjIqMLmEtZy6uAQIFK47lIgLGQABtq6+jDAxgAkaG16hsZmopblEAD8QoIwdABEglCzSlylMJIyMc1U8kA

💻 Code

const foo = {
  set bar(_) {
    return 'return value';
  }
};
const settersCanReturnValues = Object.getOwnPropertyDescriptor(foo, 'bar').set() === 'return value';
console.log(`setters can${settersCanReturnValues? '' : "'t"} return values`);

Same code, with an explicit return type:

const foo = {
  set bar(_): string {
    return 'return value';
  }
};
const settersCanReturnValues = Object.getOwnPropertyDescriptor(foo, 'bar').set() === 'return value';
console.log(`setters can${settersCanReturnValues? '' : "'t"} return values`);

🙁 Actual behavior

TypeScript compiler emits invalid JavaScript containing return type declaration syntax.

🙂 Expected behavior

TypeScript compiler supports and removes return type declarations from setters.

Additional information about the issue

[RyanCavanaugh]

All "errors" are called "errors" because we don't have anything called a "warning", since the definition of what's an error and what's a warning is subject to endless debate. You're always free to ignore an "error" with @ts-ignore.

[eligrey]

@RyanCavanaugh Ah, thank you for the clarification! I was able to bypass the error as such:

const foo = {
  set bar(_) {
    /* eslint-disable no-setter-return, @typescript-eslint/ban-ts-comment */
    // @ts-ignore
    return 'return value';
    /* eslint-enable no-setter-return, @typescript-eslint/ban-ts-comment */
  }
};
const settersCanReturnValues = Object.getOwnPropertyDescriptor(foo, 'bar').set() === 'return value';
console.log(`setters can${settersCanReturnValues? '' : "'t"} return values`);

Should I close this issue, or do you think it's worth re-scoping to improve the DX here?

[eligrey]

@RyanCavanaugh notably, set accessors cannot have return types, which is a related bug that causes actual compilation issues.

e.g.

const foo = {
  set bar(_): string {
    /* eslint-disable no-setter-return, @typescript-eslint/ban-ts-comment */
    // @ts-ignore
    return 'return value';
    /* eslint-enable no-setter-return, @typescript-eslint/ban-ts-comment */
  }
};
const settersCanReturnValues = Object.getOwnPropertyDescriptor(foo, 'bar').set() === 'return value';
console.log(`setters can${settersCanReturnValues? '' : "'t"} return values`);

[RyanCavanaugh]

Should I close this issue, or do you think it's worth re-scoping to improve the DX here?

I would take a very tactical change to the error message if someone comes up with a message that's equivalently good at conveying the point in the common case (which I think is just a person thinking they're in the getter when they're in the setter, or thinking they're inside a closure but not), but it's probably just best left alone.

[eligrey]

I re-scoped this to the return types compilation bug; feel free to further re-scope as a feature request