typescript - How to use Type?

Question

There is type:

type Filter  =  {
    <T>(array: T[], f: (item: T) => boolean): T[]
}

And concrete variable with type:

let filter: Filter;

I have tried to use it like:

filter([1,2,3], _ => _ > 2);

I got this error:

Variable 'filter' is used before being assigned.

Also I tried this:

let filter: Filter = ([1,2,3], _ => _ > 2);

Also I wonder what does it mean: _ => _ > 2 and why _ instead anothre one symbol?

For exmaple there is a realization:

function filter(array, f) {
}

How to bind this realizaton with concrete filter type?

question from:https://stackoverflow.com/questions/65870586/how-to-use-type

Answer 1

Waitting for answers