Question

Is the script below in correct form of JavaScript?

function foo(){
    return function(x){
        alert(x)
    }
}
foo()("bar");
    ↑   ↑
   There are 2 parenthesis.

It works but I don’t know if it is in a correct form.
If yes, then is that mean this is also correct?

function foo(){
    return function(){
        return function(){
            return function(){
                return function(x){
                    alert(x)
                }
            }
        }
    }
}
foo()()()()("?!?!?!");

It looks strange to me but it does work…

Answer 1

The order of function calls is shown by adding parameters:-

function foo(a){
    var A=a;
    return function(a){
        A+=a;
        return function(a){
            A+=a; 
            return function(a){
                A+=a;
                return function(a){
                    A+=a;
                    alert(A)
                }
            }
        }
    }
};
foo('a')('b')('c')('d')('e');// displays abcde

You could make the function return itself so it can be repeatedly called, eg

var foo = (function(){
    var v=1;
    return function f(x){
        return x==undefined?v: (v*=x, f);
    }
})();
foo.toString=function(){
return foo();
};
alert(foo(1)(2)(3)(4)(5)(6)(7)(8)(9)(10));

Nesting is usually to keep variables private, eg

var factorial=(function(n){
    var precog = [1,1];
    var factorial= function f(y){
        if(precog[y]==undefined){
            precog[y]=y*f(y-1);
        }
        return precog[y];
    };
    factorial(n);// initialise some precogs
    return factorial;
})(100); 

Because precog is declared in the brackets its values, calculated internally by the factorial function, cannot be messed about with.

The function assigned to the variable is called as normal:-

factorial(3);