As someone who is new to Typescript, I recently came across the following syntax:
interface Foo {
// what does age signify and
// what if it is not optional i.e () => string, age:number;
(): () => string, age?: number;
}
From what I gathered, Foo is an interface for a function where any function implementing Foo must return another function that returns a string.
However, I am still unsure about the purpose of age?: number.
In order to enhance clarity, consider using a line break and a semicolon instead of a comma (although it is intriguing that the comma is still valid based on the playground's feedback):
interface Foo {
(): () => string;
age?: number;
}
The Foo interface defines a structure for a function that:
Returns a function which itself returns a string,
Contains an optional age property that holds a value of type number.
To learn more about function types, visit this link.
Here is an example demonstrating how this interface can be utilized:
interface Foo {
(): () => string,
age?: number;
}
const f: Foo = () => () => "foo";
f.age = 42; // Take note that this assignment applies to the function
Feel free to experiment with this concept on the TypeScript Playground.
This interface can be considered quite unconventional but certainly interesting. :-)
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