Object destructuring fails if defaults are set

[jantimon]

TypeScript Version: 2.2.1 / nightly (2.2.0-dev.201xxxxx)
Try it yourself in the playground

Code

function fancyMethod({ option1:boolean = true, option2: number = 1 } = {}) {
    console.log(option1, option2);
}

fancyMethod();
fancyMethod({option2: 3});

Expected behavior:
Console log shows value of option1 and option 2

Actual behavior:
Typescript shows errors:

• Cannot find name 'option1'.
• Cannot find name 'option2'.

[ikatyang]

I think this is what you want. Object destructuring with type sometime really confuses people.

function fancyMethod({ option1 = true, option2 = 1 }: { option1?: boolean, option2?: number } = {}) {
    console.log(option1, option2);
}
fancyMethod();
fancyMethod({option2: 3});

[jantimon]

Thanks I tried this but didn't use it because of #16354

The solution now is:

function fancyMethod({ option1 = true, option2 = 1 }: object & { option1?: boolean, option2?: number } = {}) {
    console.log(option1, option2);
}

If you think of 5 options this becomes very very unreadable and creates maintenance overhead.

Is there any chance to fix it so that the following will work?

function fancyMethod({ option1:boolean = true, option2: number = 1 } = {}) {
    console.log(option1, option2);
}

[ikatyang]

This is not a valid TS code, since : in destructuring is considered renaming.

function fancyMethod({ option1: boolean = true, option2: number = 1 } = {}) { // <--
    console.log(option1, option2);
}

Additionally, {} is not assignable to { option1, option2 }, since there is no option1 and option2 in {}.

---

I think you can use type or interface to simplify the type declaration. For example:

interface X {
  option1?: boolean;
  option2?: number;
}
type NonPrimitive<T> = object & T;

function fancyMethod(x: NonPrimitive<X> = {}) {
  const {
    option1 = true,
    option2 = 1,
  } = x;
  console.log(option1, option2);
}

[jantimon]

Unfortunately the interface would be far away from the method as it is a class method.

But thanks to your explanation with the renaming I am now understanding the reason behind it 👍