Added implementation for tally

Author: Eugenie-A

Sprint-2/implement/tally.js

@@ -1,3 +1,22 @@
-function tally() {}
+function tally(arr) {
+  // Check if the input is not an array
+  if (!Array.isArray(arr)) {
+    // If it's not an array, stop the function
+    // and throw an error message
+    throw new Error("Input must be an array");
+  }
+
+  // Create an empty obkect to store our counts
+  const counts = {};
+
+  // Loop through each item in the array one by one
+  for (const item of arr) {
+    // If the item already exists in counts, add 1 to it
+    // If it doesn't exist yet (undefined), start it at 0 then add 1
+    counts[item] = (counts[item] || 0) + 1;
+  }
+  // Return the finished counts object once all items have been tallied
+  return counts;
+}
 
 module.exports = tally;