order validation

js/order.js

@@ -1,16 +1,33 @@
+function calculate_total() {
+  var total = 0
+  items = document.getElementsByClassName("order_item")
+  for (const item of items){
+    price = parseInt(item.dataset.price)
+    count = parseFloat(item.value)
+    total += count * price
+  }
+  document.getElementById("total_price").innerText = total + "zł"
+}
+
 function min(a, b) {
   if (a > b) {
     return a
   }
   return b
 }
+
 function increase(id) {
   input = document.getElementById(id)
   step = parseFloat(input.step)
   input.value= min(parseFloat(input.value)+step, 0)
+  calculate_total()
 }
+
 function decrease(id) {
   input = document.getElementById(id)
   step = parseFloat(input.step)
   input.value= min(parseFloat(input.value)-step, 0)
+  calculate_total()
 }
+
+calculate_total()