If an interface property is set as (), what significance does it hold?

While exploring the Vue.js source code located at

packages/reactivity/src/effects.ts
, I came across this snippet:

export interface ReactiveEffectRunner<T = any> {
  (): T
  effect: ReactiveEffect
}

I'm curious, what does () signify in the code block?

Answer №1

If you are looking to create a function with additional properties, you can utilize this specific pattern.

() signifies that the object implementing this interface will act as a callable function without any required parameters.

effect indicates that there is an added property named effect.

A sample code snippet from the documentation:

type DescribableFunction = {
  description: string;
  (someArg: number): boolean;
};
function doSomething(fn: DescribableFunction) {
  console.log(fn.description + " returned " + fn(6));
}

Explore more about call signatures

Answer №2

It signifies that the type is capable of being executed as a function.

For instance:

declare const fn: ReactiveEffectRunner<{ abc: number }>

const result = fn() // { abc: number }
fn.effect // ReactiveEffect

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