completed the JavaScript calculator

Author: Matej Jeglic

days/025-028-javascript/demo/calculator/index-template.html

@@ -38,7 +38,27 @@ <h1>Basic JS Calculator</h1>
 
   <script type="text/javascript">
   function doCalculation(){
-    // you code
+    let num1 = parseInt(document.getElementById('num1').value);
+    let num2 = parseInt(document.getElementById('num2').value);
+    let select = document.getElementById('operator');
+    let operator = select.selectedOptions[0].getAttribute('name');
+
+    math = {
+      '+' : function(x, y){return x + y},
+      '-' : function(x, y){return x - y},
+      '*' : function(x, y){return x * y},
+      '/' : function(x, y){return x / y},
+    };
+    
+    let result = math[operator](num1, num2);
+    let result_element = document.getElementById('result');
+
+    if(isNaN(result) || !isFinite(result)){
+      result_element.style.color = 'red';
+    } else {
+      result_element.style.color = 'green';
+    }
+    result_element.innerHTML = result;
   }
   </script>