How to specify object type in function call

Question

If I am calling a function that takes any how do I specify the type of an object literal that is passed in directly (without creating a local variable). This doesn't work:

      aMessageChannel.port1.postMessage({
        foo: 1,
        bar: 2,
      }: MyMessageType);

Why do you need to specify the type of the parameter if the function doesn't require it? — Aron
– Aron, Commented Apr 21, 2020 at 13:33

Aron · Accepted Answer · 2020-04-21 13:48:46Z

1

I'm not sure why you would need to specify an object's type at the place where it is called, you would usually do that in the function definition.

In the case where you are calling an outside function that accepts any - and because it's someone else's code you cannot change the function's signature - you can define your object with a type declaration first and then pass it into the function.

// if obj does not have the right shape to be a MyMessageType then the error will display here
const obj: MyMessageType = {
  foo: 1,
  bar: 2,
}

aMessageChannel.port1.postMessage(obj);

answered Apr 21, 2020 at 13:48

Aron

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2 Comments

Timmmm Over a year ago

Yes this is an obvious workaround, which is why I specifically said an object literal that is passed in directly (without creating a local variable).

Aron Over a year ago

TypeScript doesn't have syntax for that. Sorry.

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