We usually call a function by using a set on parenthesis after its name eg. fun() but what if our function returned a function? In that case you would be able to call it again

function hello(){
    console.log("Hello");
    return () => console.log(" world");
}
hello()();

It looks a lot normal if we use a variable in between

function hello(){
    console.log("Hello");
    return () => console.log(" world");
}
let func = hello(); //receiving the function returned from hello
func();

but in we try to call the function third time it will give us error.

but what if your function returned itself? in that case when ever we call it we are again getting a function returned so can can keep calling it infinitely

function hello(){
    console.log("Hello");
    return hello;
}
hello()()()()()()()()()()()();