diff --git a/javascript/chronometer.js b/javascript/chronometer.js
index 7a1349680..8f13ac8e8 100644
--- a/javascript/chronometer.js
+++ b/javascript/chronometer.js
@@ -1,34 +1,69 @@
 class Chronometer {
   constructor() {
     // ... your code goes here
+    this.currentTime = 0;
+    this.intervalId = null;
   }
 
   start(callback) {
     // ... your code goes here
+    if (!this.intervalId) {
+      this.intervalId = setInterval(() => {
+        this.currentTime += 1
+      }, 1000)
+    }
   }
 
   getMinutes() {
     // ... your code goes here
+    if (this.currentTime === 0) {
+      return 0;
+    } else {
+      return Math.floor(this.currentTime / 60)
+    }
   }
 
   getSeconds() {
     // ... your code goes here
+    if (this.currentTime === 0) {
+      return 0;
+    } else {
+      return this.currentTime % 60
+    }
   }
 
   computeTwoDigitNumber(value) {
     // ... your code goes here
+    if (value >= 10) {
+      return value.toString();
+    } else {
+      return ('0' + value).toString()
+    }
   }
 
   stop() {
     // ... your code goes here
+    return clearInterval(this.intervalId);
   }
 
   reset() {
     // ... your code goes here
+    return this.currentTime = 0;
   }
 
   split() {
     // ... your code goes here
+   if (this.currentTime >= 60) {
+    let minutesNum = this.getMinutes();
+    let secondsNum = this.getSeconds();
+    let minutes = this.computeTwoDigitNumber(minutesNum);
+    let seconds = this.computeTwoDigitNumber(secondsNum); 
+    return `${minutes}:${seconds}`
+   } else {
+    let secondsNum = this.getSeconds();
+    let seconds = this.computeTwoDigitNumber(secondsNum);
+    return `00:${seconds}`
+   }
   }
 }
 
@@ -36,4 +71,4 @@ class Chronometer {
 /* Environment setup. Do not modify the below code. */
 if (typeof module !== 'undefined') {
   module.exports = Chronometer;
-}
+}
\ No newline at end of file
diff --git a/javascript/index.js b/javascript/index.js
index fb3a43ab4..0927ed6de 100644
--- a/javascript/index.js
+++ b/javascript/index.js
@@ -15,10 +15,12 @@ const splitsElement = document.getElementById('splits');
 
 function printTime() {
   // ... your code goes here
+
 }
 
 function printMinutes() {
   // ... your code goes here
+  
 }
 
 function printSeconds() {
@@ -57,6 +59,26 @@ function setResetBtn() {
 // Start/Stop Button
 btnLeftElement.addEventListener('click', () => {
   // ... your code goes here
+  if (btnLeftElement.classList.contains('start')) {
+    btnLeftElement.classList.remove('start');
+    btnLeftElement.classList.add('stop');
+    btnLeftElement.innerHTML = 'STOP';
+    btnLeftElement.classList.remove('reset');
+    btnLeftElement.classList.add('split');
+    btnRightElement.innerHTML = 'SPLIT';
+
+    chronometer.start();
+    
+  } else if (btnLeftElement.classList.contains('stop')) {
+    btnLeftElement.classList.remove('stop');
+    btnLeftElement.classList.add('start')
+    btnLeftElement.innerHTML = 'START';
+    btnRightElement.classList.remove('split');
+    btnRightElement.classList.add('reset');
+    btnRightElement.innerHTML = 'RESET';
+
+    chronometer.stop();
+  }
 });
 
 // Reset/Split Button
diff --git a/package.json b/package.json
index 879644e13..d6e8b15ed 100644
--- a/package.json
+++ b/package.json
@@ -7,7 +7,7 @@
     "test:watch": "jest --watchAll --verbose=false"
   },
   "devDependencies": {
-    "jest": "^26.6.3",
+    "jest": "^29.7.0",
     "jest-html-reporter": "^3.3.0",
     "jest-junit": "^12.0.0"
   },