add median.js

Author: asandagwala

Sprint-1/fix/median.js

@@ -6,9 +6,24 @@
 // or 'list' has mixed values (the function is expected to sort only numbers).
 
 function calculateMedian(list) {
-  const middleIndex = Math.floor(list.length / 2);
-  const median = list.splice(middleIndex, 1)[0];
+  if (!Array.isArray(list)){
+    return null;
+  }
+  const numbersOnly = list.filter(item => typeof item === "number");
+  if (numbersOnly.length === 0){
+    return null;
+  }
+  numbersOnly.sort((a,b)=>a-b)
+
+  const middleIndex = Math.floor(numbersOnly.length / 2);
+  if (numbersOnly.length % 2 === 0){
+    return (numbersOnly[middleIndex-1] + numbersOnly[middleIndex])/2;
+  } else {
+    return numbersOnly[middleIndex];
+  }
+  const median = numbersOnly.splice(middleIndex, 1)[0];
   return median;
+ 
 }
 
 module.exports = calculateMedian;