Is it required to define parameters in a Javascript function?

Question

Is it required to define parameters in a javascript function? My question is regarding my comchoice function down below, where I simply use the open and close parentheses without giving any parameters that can be changed.

I listed my full code for the script just for reference

var userChoice = prompt("Do you choose rock, paper or scissors?");
var computerChoice = Math.random();
var compchoice = function ()
{
    if (computerChoice <= 0.34) 
    {
        return computerChoice = "Rock";
    } 
    else if(0.35 <= computerChoice <= 0.67) 
    {
        return computerChoice = "Paper";
    } 
    if (0.68 <= computerChoice <= 1)
    {
        return computerChoice = "Scissors";
    }
};

compchoice();

var compare = function (choice1, choice2)
{
    if (choice1 === choice2)
    {
        return alert("The result is a tie!");
    }

    if (choice1 === "Rock")
    {
        if (choice2 === "Scissors")
        {
            return alert("Rock wins!");
        }
        else if (choice2 === "Paper")
        {
            return alert("Paper wins!");
        }
    }
    else if (choice1 === "Scissors")
    {
        if (choice2 === "Rock")
        {
            return alert("Rock wins!");
        }
        else if (choice2 === "Paper")
        {
            return alert("Schissors wins!");
        }
    }
};

compare(userChoice, computerChoice);

Answer 1

No, it is not necessary to pass parameter, function can be with no parameter. In your case function is accessing the outer variables with closures.

Answer 2

What you can do is something like the following:

function RandomFunction(){
   alert( arguments[0] );
   console.log( arguments[1] );
}

RandomFunction( 'Hello World', 'Good bye' );

And find the arguments for the function in the "arguments" variable within a function. Thus, no need to declare the argument, but declaring them is always a great way to go.

Also, instead of using traditional arguments, you can pass in an object to be used as an extensible list of objects:

function AnotherFunction( x ){
   alert( x.message );
}

AnotherFunction( {message: 'Hello Again, world'} );

Answer 3

As per the Function Definition Syntax

FunctionExpression :
function Identifier _opt ( FormalParameterList _opt ) { FunctionBody } _{(ES5 §13)}

In a function expression you can ommit the identifier as well as the parameters.

Hence your code is syntactically valid.