Typescript how to type the rest of parameters in object

Question

  function test(data){
      console.log(data)
  }

  test({comments: 'hi', eat: true, sleep: true})

In the test function, I am sure of the comment argument will appear, where as for other arguments, the properties might be dynamic but the value will be of boolean type,

  test({comments: 'hi', drink: true, sleep: true})

considering this situation, how should I correctly type data? I have tried something like this, but it seems wrong

function(data: {data: {comments: string, [key: string]: boolean})

Is the question, then, "what type do I give to the parameter `data`, which should be an object with at least one property named `comments` of type string, but which could have lots of other properties that I don't care about"? — Ray Toal, Nov 26 '20 at 09:43
If you don't care about the other properties, then `type DataType = { comments: string; [key: string]: unknown; };` will work. Ref: https://stackoverflow.com/a/33860616 — Yoshi, Nov 26 '20 at 09:50
Sorry about the above comment. I know that other properties value would be boolean — sridhar.., Nov 26 '20 at 09:53
Ah good, then it is not the same as this question? https://stackoverflow.com/a/42724170/831878 Because you want to restrict all the other properties to boolean? — Ray Toal, Nov 26 '20 at 09:54
That solution doesn't seem to work, as soon as i keep boolean, vs code editor is throwing errors — sridhar.., Nov 26 '20 at 09:58
Right, right, your question is indeed different (and pretty cool). Looks like intersection types have potential, but fall short. More info here: https://github.com/microsoft/TypeScript/issues/20597. — Ray Toal, Nov 26 '20 at 10:05
Relevant issue https://github.com/microsoft/TypeScript/issues/17867 — Aleksey L., Nov 26 '20 at 12:40

score 1 · Answer 1 · answered Nov 26 '20 at 10:55

I can suggest you some kind of workaround:

function test<T extends {
  [key: string]: any;
}>(data: { comments: unknown } & { [key in keyof T]: key extends "comments" ? string : boolean }) {
  const comments = data.comments as string;
  console.log(comments);
  console.log(data.eat);
  console.log(data.sleep);
}

test({comments: "hi"}); // works
test({comments: "hi", eat: true}); // works
test({comments: true}); // doesn't works
test({comments: 5}); // doesn't works
test({comments: "hi", eat: "true"}); // doesn't works
test({comments: "hi", eat: 5}); // doesn't works

It typed well outside of the function's body, but in function's body to type data.comments correctly you should add some narrowing.

Typescript how to type the rest of parameters in object

1 Answers1