Javascript fails on old Windows Firefox

Question

I have built an order inquiry form that has a few Javascript-driven features. I've got this form working on every browser I can test, which is Win 10 and a few Mac operating systems. My client is still using Windows XP, and he says these two features are not working:

1. increase price of an item with a radio button option

2. calculate subtotal at the bottom of the page after collecting all of the prices and quantities from the various items.

Before I tell him that I can't support XP, I'm wondering if there's something in my script that is a known to fail in Firefox on Windows XP (and hopefully has a workaround). I've checked the method documentation online, and I'm not seeing it. Here are the various scripts that I'm using. These are pure Javascript, just to see if I can do it.

The subtotal recalculation is triggered every time an item quantity changes.

/************************************************
 *              Wide Option
 ************************************************/

function subtractWideOption() { // below traverse DOM from radio button to price
  var priceSpan = event.target.parentNode.parentNode.nextElementSibling.firstElementChild;
  if (priceSpan.className.indexOf("wider") !== -1) { // test if option is already set
    var currentPrice = parseInt(priceSpan.innerHTML.slice(1), 10); // remove $ sign and parse
    var newPrice = currentPrice - 25; // remove cost for option
    priceSpan.innerHTML = "$" + newPrice; // add $ sign
    priceSpan.className = priceSpan.className.replace(" wider",""); // remove option class
    priceSpan.className += " std"; // add standard class
  } else {
    return;
  }
}

function addWideOption() {
  var priceSpan = event.target.parentNode.parentNode.nextElementSibling.firstElementChild;
  if (priceSpan.className.indexOf("std") !== -1) {
    var currentPrice = parseInt(priceSpan.innerHTML.slice(1), 10);
    var newPrice = currentPrice + 25;
    priceSpan.innerHTML = "$" + newPrice;
    priceSpan.className = priceSpan.className.replace(" std","");
    priceSpan.className += " wider";
  } else {
    return;
  }
}



/************************************************
 *              Order Subtotal
 ************************************************/

var qtyBtns = document.getElementsByClassName("qty"); // collect all qty inputs
var subTotal = document.getElementById("oi_subt");

function recalcSubtotal() {
  var subT = 0;
  for (var i = 0; i < qtyBtns.length; i++) { // below traverse DOM from input to price
    var priceHTML = qtyBtns[i].parentNode.previousElementSibling.firstElementChild.innerHTML;
    if (priceHTML == "TBD") { // one custom item with TBD price is ignored
      price = "0"
    } else {
      priceHTML = priceHTML.replace(",",""); // remove comma from price
      var price = parseInt(priceHTML.slice(1), 10); // remove $ sign and parse
    };
    var qty = parseInt(qtyBtns[i].value, 10);
    subT += (price * qty); // add up all items ordered
    subTotal.innerHTML = "$" + subT;
  }
}

Answer 1

You are binding your event handlers like this:

var stepupBtns = document.getElementsByClassName("steppingUp");

for (var i = 0; i < stepupBtns.length; i++) {
  stepupBtns[i].onclick = function(){
    var valueOf = this.previousElementSibling.value;
    valueOf = ++valueOf;
    this.previousElementSibling.value = valueOf;
    event.preventDefault();
    recalcSubtotal();
  }
}

In these functions, note that the event variable is not defined anywhere. The event variable should be passed in your function definition:

  stepupBtns[i].onclick = function(event){

You should do this on all of your handlers.

More information can be found here: https://stackoverflow.com/a/20522980