Factorials/Combinations Yields NaN When Not Supposed To

I am solving for y Choose p combinations. I am a beginner with Javascript.

I have produced this definition of the factorial function: It was inteded to do x * (x-1) * (x-2) ... * 1.

function factorial(z)
{
    var product = z;
    if (z == 0)
    {
        return 1;
    }
    else
    {
        for (var m = 1; m < z; m++)
        {
            product = m * product;
            return product;
        }
    }
}

I then have this function, which uses the factorial function.

function placeBoxes()
{
    var ids = 0;
    for (var y = 0; y < (numOfRows-1); y++)
    {
        for (var p = 0; p < (y+1); p++, ids++)
        {
            x = document.createElement('div');
            x.className = "box";
            x.id = ids;
            x.innerHTML = (factorial(y))/((factorial(y-p))*(factorial(p)));
            document.getElementByI开发者_开发技巧d('holdsBoxes').appendChild(x);
        }
    }
}

It is supposed to choose the combinations. For experimental purposes, numOfRows is realistically between 5 and 30. 0C0 1C0 1C1 2C0 2C1 2C2 and so on... This is equivalent to 1, 1, 1, 1, 2, 1 and so on...

Does anyone know what I have done wrong? I am getting NaN instead of a value for the second, third, fifth, eighth, ninth, and many other values.

Edit: Thank you everyone! The problem is solved. The factorial function was messed up.

Change

    for (var m = 1; m < z; m++)
    {
        product = m * product;
        return product;
    }

To

    for (var m = 1; m < z; m++)
    {
        product = m * product;
    }
    return product;

You're never completing the loop

for (var m = 1; m < z; m++)
{
    product = m * product;
    return product;
}

Your returning product inside your loop. Are you sure about this? Don't you want to return product outside your loop?

This is also the cause of your NaN. What if z is 1 ? then m < z is m < 1 and thats always false. So that loop body is never being called. and the return statement is never called.

So the function returns undefined. And undefined * 1 === NaN

I believe that the factorial function is incorrect. Try changing it to this:

function factorial(z)
{
    var product = z;
    if (z == 0)
    {
        return 1;
    }
    else
    {
        for (var m = 1; m < z; m++)
        {
            product = product*(product - m);
        }
        return product;
    }
}