Are the object properties defined correctly in the example?

Question

JavaScript

There is a code, and I have doubts about its correctness. Namely, in the getCounter function, we define the let counter function, in which we later define properties, without calling it in the getCounter function itself, so, is it possible to set properties for the function in this way, without knowing what else it will return . And what does it do <counter>before the function in this example?

interface Counter {
    (start: number): string;
    interval: number;
    reset(): void;
}
 
function getCounter(): Counter {
    let counter = <counter>function (start: number) { };
    counter.interval = 123;
    counter.reset = function () { };
    return counter;
}
 
let c = getCounter();
c(10);
c.reset();
c.interval = 5.0;
</counter>