Adding two javascript functions(depending on input) - html

Question

I have put together a calculator what calculates a price, depending on user input. It works fine with one input, but now I have to scale it a little with a second user input. But here's the catch: the user might not want to put anything to the field, so it will be empty. And that's the thing that brakes my code. I could duplicate the calculator function and return the values and add those two together in a third function, but it will not work when there's an empty value.
Just for the sake of it, some trivial HTML code:
//When I only calculate with this user input, its easy
<input type="text" id="rocktext"><br>
// But how to consider this and do the same exact calculations like with the
//first one and add those two result together?
<input type="text" id="rocktext2"><br>
The code in the end should look like:
Take first user input, calculate the price(like in code below)
IF(!!) there is a second user input, calculate the price and add it to
the first one
Am I being a moron to try it with JS or just a moron in the firstplace?
Hope to hear from You, guys!
J.
The initial JS code is as follows:
function priceCalc() {
var inputs = document.getElementById("rocktext").value;
var length = inputs.length;
var accept = 6;
var initPrice = 8;
if (inputs<=accept){
// Since the code is much simpler right now i just put the result in HTML as follows:
document.getElementById("rockpricetotal").innerHTML = initPrice + " dollars";
//I can also return the the value calculated here like so:
//retVal = initPrice;
}
else {
var intLength = parseInt(length, 10);
var lengthGap = intLength - accept;
var totals = lengthGap * 0.8 + initPrice;
var prec = totals.toPrecision(3);
// Since the code is much simpler right now i just put the result in HTML as follows:
document.getElementById("rockpricetotal").innerHTML = prec + " dollars";
// Here also the return clause can be possible with the calculation result like so:
//retVal = prec;
}
// And the final return as an alternative to the innerHTML :
// return retVal;
}

Answer 1

Making it scalable, you can add a class to all the inputs which may be in the function (something like calcInput), so you iterate all of them and if the value isn't empty (and if it's a valid number), you put it in the calculation.
Or you can just verify if the second input is empty, if so, calls functionOne, if not, calls functionTwo:
function twoDifferentWays() {
var valueOne = document.querySelector("#rocktext").value;
var valueTwo = document.querySelector("#rocktext2").value;
if (!!valueTwo && !isNaN(valueTwo)) {
callsFunctionOne(valueOne, valueTwo);
} else {
callsFunctionTwo(valueOne, valueTwo);
}
}