diff --git a/javascript/chronometer.js b/javascript/chronometer.js
index 7a1349680..4afdaf4a0 100644
--- a/javascript/chronometer.js
+++ b/javascript/chronometer.js
@@ -1,39 +1,44 @@
 class Chronometer {
   constructor() {
-    // ... your code goes here
+    this.currentTime = 0;
+    this.intervalId = null;
   }
 
   start(callback) {
-    // ... your code goes here
+    this.intervalId = setInterval(() => {
+      this.currentTime++;
+      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);
   }
 
   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') {
   module.exports = Chronometer;
 }
diff --git a/javascript/index.js b/javascript/index.js
index fb3a43ab4..73c7fe3c8 100644
--- a/javascript/index.js
+++ b/javascript/index.js
@@ -1,65 +1,80 @@
 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');
+// DOM elements
+const btnLeft = document.getElementById('btnLeft');
+const btnRight = document.getElementById('btnRight');
+const minDec = document.getElementById('minDec');
+const minUni = document.getElementById('minUni');
+const secDec = document.getElementById('secDec');
+const secUni = document.getElementById('secUni');
+const splits = document.getElementById('splits');
 
 function printTime() {
-  // ... your code goes here
+  printMinutes();
+  printSeconds();
 }
 
 function printMinutes() {
-  // ... your code goes here
+  const minutes = chronometer.computeTwoDigitNumber(chronometer.getMinutes());
+  minDec.innerText = minutes[0];
+  minUni.innerText = minutes[1];
 }
 
 function printSeconds() {
-  // ... your code goes here
-}
-
-// ==> BONUS
-function printMilliseconds() {
-  // ... your code goes here
+  const seconds = chronometer.computeTwoDigitNumber(chronometer.getSeconds());
+  secDec.innerText = seconds[0];
+  secUni.innerText = seconds[1];
 }
 
 function printSplit() {
-  // ... your code goes here
+  const li = document.createElement('li');
+  li.className = 'list-item';
+  li.innerText = chronometer.split();
+  splits.appendChild(li);
 }
 
 function clearSplits() {
-  // ... your code goes here
+  splits.innerHTML = '';
 }
 
 function setStopBtn() {
-  // ... your code goes here
+  btnLeft.innerText = 'STOP';
+  btnLeft.className = 'btn stop';
 }
 
 function setSplitBtn() {
-  // ... your code goes here
+  btnRight.innerText = 'SPLIT';
+  btnRight.className = 'btn split';
 }
 
 function setStartBtn() {
-  // ... your code goes here
+  btnLeft.innerText = 'START';
+  btnLeft.className = 'btn start';
 }
 
 function setResetBtn() {
-  // ... your code goes here
+  btnRight.innerText = 'RESET';
+  btnRight.className = 'btn reset';
 }
 
-// Start/Stop Button
-btnLeftElement.addEventListener('click', () => {
-  // ... your code goes here
+btnLeft.addEventListener('click', () => {
+  if (btnLeft.classList.contains('start')) {
+    chronometer.start(printTime);
+    setStopBtn();
+    setSplitBtn();
+  } else {
+    chronometer.stop();
+    setStartBtn();
+    setResetBtn();
+  }
 });
 
-// Reset/Split Button
-btnRightElement.addEventListener('click', () => {
-  // ... your code goes here
+btnRight.addEventListener('click', () => {
+  if (btnRight.classList.contains('reset')) {
+    chronometer.reset();
+    printTime();
+    clearSplits();
+  } else {
+    printSplit();
+  }
 });