diff --git a/javascript/chronometer.js b/javascript/chronometer.js
index 7a13496..76f604e 100644
--- a/javascript/chronometer.js
+++ b/javascript/chronometer.js
@@ -1,37 +1,47 @@
 class Chronometer {
   constructor() {
-    // ... your code goes here
+    this.currentTime = 0;
+    this.intervalId = null;
   }
 
   start(callback) {
-    // ... your code goes here
+    this.intervalId = setInterval(() => {
+      this.currentTime += 1;
+      if (callback) {
+        callback();
+      }
+    }, 1000);
   }
 
   getMinutes() {
-    // ... your code goes here
+    return Math.floor(this.currentTime / 60);
   }
 
   getSeconds() {
-    // ... your code goes here
+    return this.currentTime % 60;
   }
 
   computeTwoDigitNumber(value) {
-    // ... your code goes here
+    return value < 10 ? `0${value}` : `${value}`;
   }
 
   stop() {
-    // ... your code goes here
+    clearInterval(this.intervalId);
+    this.intervalId = null;
   }
 
   reset() {
-    // ... your code goes here
+    this.currentTime = 0;
   }
 
   split() {
-    // ... your code goes here
+    const minutes = this.computeTwoDigitNumber(this.getMinutes());
+    const seconds = this.computeTwoDigitNumber(this.getSeconds());
+    return `${minutes}:${seconds}`;
   }
 }
 
+
 // The following is required to make unit tests work.
 /* Environment setup. Do not modify the below code. */
 if (typeof module !== 'undefined') {
diff --git a/javascript/index.js b/javascript/index.js
index fb3a43a..067ba99 100644
--- a/javascript/index.js
+++ b/javascript/index.js
@@ -1,65 +1,81 @@
 const chronometer = new Chronometer();
 
-// get the buttons:
 const btnLeftElement = document.getElementById('btnLeft');
 const btnRightElement = document.getElementById('btnRight');
 
-// get the DOM elements that will serve us to display the time:
 const minDecElement = document.getElementById('minDec');
 const minUniElement = document.getElementById('minUni');
 const secDecElement = document.getElementById('secDec');
 const secUniElement = document.getElementById('secUni');
-const milDecElement = document.getElementById('milDec');
-const milUniElement = document.getElementById('milUni');
 const splitsElement = document.getElementById('splits');
 
 function printTime() {
-  // ... your code goes here
+  printMinutes();
+  printSeconds();
 }
 
 function printMinutes() {
-  // ... your code goes here
+  const minutes = chronometer.computeTwoDigitNumber(chronometer.getMinutes());
+  minDecElement.innerHTML = minutes[0];
+  minUniElement.innerHTML = minutes[1];
 }
 
 function printSeconds() {
-  // ... your code goes here
-}
-
-// ==> BONUS
-function printMilliseconds() {
-  // ... your code goes here
+  const seconds = chronometer.computeTwoDigitNumber(chronometer.getSeconds());
+  secDecElement.innerHTML = seconds[0];
+  secUniElement.innerHTML = seconds[1];
 }
 
 function printSplit() {
-  // ... your code goes here
+  const splitTime = chronometer.split();
+  const li = document.createElement('li');
+  li.className = 'list-item';
+  li.innerHTML = splitTime;
+  splitsElement.appendChild(li);
 }
 
 function clearSplits() {
-  // ... your code goes here
+  splitsElement.innerHTML = '';
 }
 
 function setStopBtn() {
-  // ... your code goes here
+  btnLeftElement.innerHTML = 'STOP';
+  btnLeftElement.className = 'btn stop';
 }
 
 function setSplitBtn() {
-  // ... your code goes here
+  btnRightElement.innerHTML = 'SPLIT';
+  btnRightElement.className = 'btn split';
 }
 
 function setStartBtn() {
-  // ... your code goes here
+  btnLeftElement.innerHTML = 'START';
+  btnLeftElement.className = 'btn start';
 }
 
 function setResetBtn() {
-  // ... your code goes here
+  btnRightElement.innerHTML = 'RESET';
+  btnRightElement.className = 'btn reset';
 }
 
-// Start/Stop Button
 btnLeftElement.addEventListener('click', () => {
-  // ... your code goes here
+  if (btnLeftElement.classList.contains('start')) {
+    chronometer.start(printTime);
+    setStopBtn();
+    setSplitBtn();
+  } else {
+    chronometer.stop();
+    setStartBtn();
+    setResetBtn();
+  }
 });
 
-// Reset/Split Button
 btnRightElement.addEventListener('click', () => {
-  // ... your code goes here
+  if (btnRightElement.classList.contains('reset')) {
+    chronometer.reset();
+    printTime();
+    clearSplits();
+  } else {
+    printSplit();
+  }
 });