Question 134819 in Visual Studio Code Question posted in
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Visual Studio Code – How can I describe and call a function of a type of object in TypeScript?

Well, I am learning TypeScript right now and am getting a problem. I do not know the reason.

When I call the function of an object, Visual Studio Code throws an error that type of {} has no call signatures.

I’ve tried to describe the type of function, but I failed.

console.log(b.<object>fn())

let b: { name: string; fn: {} }

b = {
  name: 'derek',
  fn: (): void => {
    console.log('i am a function')
  }
}

console.log(b.fn())
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3

Answers


  1. 0

    fn should be of type () => void based on your definition:

    let b: { name: string; fn: () => void }

    playground

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  2. 0

    In TypeScript, functions are usually typed using arrow notation to describe the function signature. So the type of a parameterless function that has no return value would be () => void.

    In your example, the property fn of b should have that type:

    let b: { name: string; fn: () => void }

    {} in TypeScript is used to represent something that can be any non-nullish value (anything that isn’t null or undefined), meaning it’s not guaranteed to be a callable function.

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  3. 0

    It looks like you are trying to call the fn function on the b object, but you have not defined the type of the fn function.

    To fix this error, you can define the type of the fn function by specifying the parameters and return type.

    For example:

    let b: { name: string; fn: (x: number, y: number) => string }

b = {
  name: 'derek',
  fn: (x: number, y: number): string => {
    return `The result is ${x + y}`
  }
}

console.log(b.fn(1, 2))  //"The result is 3"
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