Implement repeatStr function with error handling

Re-implemented repeatStr function to repeat a string a specified number of times without using String.prototype.repeat. Added error handling for negative counts.

Author: mrafeie

Sprint-3/2-practice-tdd/repeat-str.js

@@ -1,7 +1,15 @@
-function repeatStr() {
-  // Your implementation of this function must *not* call String.prototype.repeat (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat).
-  // The goal is to re-implement that function, not to use it.
-  return "hellohellohello";
+function repeatStr(str, count) {
+  if (count < 0) {
+    throw new Error("Count cannot be negative");
+  }
+
+  let result = "";
+
+  for (let i = 0; i < count; i++) {
+    result += str;
+  }
+
+  return result;
 }
 
 module.exports = repeatStr;