How to get argument types from Window Object functions in Typescript

Question

I would like to know how I can in typescript acquire all the args types of each function of the object window.

Below as you will see is the type that I have implemented but apparently I am doing it wrong ..

If someone can help me I will appreciate it.

type Arguments<F extends Function> = F extends (...args: infer A) => any ? A : never;

const x = (window: Window) => window.alert('hola')
type TestArguments = Arguments<typeof x>; 

Answer 1

Your TestArguments variable is an array of arguments (it even is plural). You need to either:

Access the first element:

type Arguments<F extends Function> = F extends (...args: infer A) => any ? A : never;

const x = (window: Window) => window.alert('hola')
type TestArgument = Arguments<typeof x>[0];

Or infer only the first argument.

type FirstArgument<F extends Function> = F extends (firstArg: infer A) => any ? A : never;

const x = (window: Window) => window.alert('hola')
type TestArgument = FirstArgument<typeof x>; 

TypeScript Playground

Finally, to get only the functions of your function, you would do this:

type OnlyFunctions<T> = Pick<T, { [k in keyof T]: T[k] extends Function ? k : never }[keyof T]>

This basically maps through the Window object, setting never to variables that are not functions. Then, get the keys of that array, and use it to construct a new array (using Pick), which only has those keys.

You can combine everything using:

type OnlyFunctionsFromFirstArgument = OnlyFunctions<FirstArgument<typeof x>>;

TypeScript Playground