Build a Stopwatch using React in 20 minutes! ⏱

#reactjs #tutorial #course
This is a beginner's React project that uses only useState, useEffect, and useRef.
00:00:00 imports/exports
00:01:17 useState + useRef
00:02:48 function declarations
00:03:39 HTML
00:05:45 CSS
00:11:45 functions
00:14:06 useEffect()
00:16:10 formatTime()
00:19:19 conclusion

[@BroCodez]

import Stopwatch from './Stopwatch.jsx';
function App() {
return ();
}
export default App;
import React, {useState, useEffect, useRef} from 'react';
function Stopwatch(){
const [isRunning, setIsRunning] = useState(false);
const [elapsedTime, setElapsedTime] = useState(0);
const intervalIdRef = useRef(null);
const startTimeRef = useRef(0);
useEffect(() => {
if(isRunning){
intervalIdRef.current = setInterval(() => {
setElapsedTime(Date.now() - startTimeRef.current);
}, 10);
}
return () => {
clearInterval(intervalIdRef.current);
}
}, [isRunning]);
function start(){
setIsRunning(true);
startTimeRef.current = Date.now() - elapsedTime;
}
function stop(){
setIsRunning(false);
}
function reset(){
setElapsedTime(0);
setIsRunning(false);
}
function formatTime(){
let hours = Math.floor(elapsedTime / (1000 * 60 * 60));
let minutes = Math.floor(elapsedTime / (1000 * 60) % 60);
let seconds = Math.floor(elapsedTime / (1000) % 60);
let milliseconds = Math.floor((elapsedTime % 1000) / 10);
hours = String(hours).padStart(2, "0");
minutes = String(minutes).padStart(2, "0");
seconds = String(seconds).padStart(2, "0");
milliseconds = String(milliseconds).padStart(2, "0");
return `${minutes}:${seconds}:${milliseconds}`;
}
return(

{formatTime()}

Start
Stop
Reset


);
}
export default Stopwatch
body{
display: flex;
flex-direction: column;
align-items: center;
background-color: hsl(0, 0%, 95%);
}
.stopwatch{
display: flex;
flex-direction: column;
align-items: center;
border: 5px solid;
border-radius: 50px;
background-color: white;
padding: 30px;
}
.display{
font-size: 5rem;
font-family: monospace;
font-weight: bold;
color: hsl(0, 0%, 30%);
text-shadow: 2px 2px 2px hsla(0, 0%, 0%, 0.75);
margin-bottom: 25px;
}
.controls button{
font-size: 1.5rem;
font-weight: bold;
padding: 10px 20px;
margin: 5px;
min-width: 125px;
border: none;
border-radius: 10px;
cursor: pointer;
color: white;
transition: background-color 0.5s ease;
}
.start-button{
background-color: hsl(115, 100%, 40%);
}
.start-button:hover{
background-color: hsl(115, 100%, 35%);
}
.stop-button{
background-color: hsl(10, 90%, 50%);
}
.stop-button:hover{
background-color: hsl(10, 90%, 45%);
}
.reset-button{
background-color: hsl(205, 90%, 60%);
}
.reset-button:hover{
background-color: hsl(205, 90%, 55%);
}

[@RealRower1]

hey Bro Code can you make a course about lua @BroCodez

[@avanguly4843]

i dont think he plays roblox lil bro@@RealRower1

[@l213dhanesh3]

Where are u code bro help me with angular js..... Missing u bro mava

[@-_SleepAndEat_-]

Bro can you do Kali Linux ?

[@YoniYo12]

Best project tutorial ever! simple and to the point, thanks Bro

[@ejebeueh9113]

So this bro gets 830 views while dancing toys get millions what a shame

[@RadheKrishno-xr8ew]

Let the good things be with us 😁

[@Dylan12kpo1k2pDylan]

You beautiful man, keep adding to this playlist

[@siddhantraj9425]

Thanks man. Helped a lot

[@samaali6589]

Keep it up! Appreciate the efforts

[@tofu7736]

Just waiting for 12:00:00 hours React video to come
By the way I have watched all the web development courses you’ve been uploading.
Thanks bro because of you i can understand and learn web dev.
Big heart for BRO ARMY 💜💜💜💜💜

[@nesa6582]

Its over, it is only 4h. :D

[@abdulbasit9364]

Bro you drop ur crown 👑❤

[@rishabhkedia9304]

Please make Reactjs projects as well

[@user-jr7lt8fk2b]

hey bro
can u make a course about laravel for beginners
u r so good and now i only can learn anything from you
thanks a lot

[@java_learn6447]

Sir please upload react form validations

[@Ashwini243]

Hi, I am based in the USA.I really love your videos and they are interview oriented.
Can you explain why you used useRef variable?

[@Prateek_Mantry]

useRef is used to stop re-rendering your component when the variable(ref) is changed, which is not possible using useState().

[@worldnothing3721]

bro are bringing backend development also

[@HabibHaris-fe7fy]

please sir make a playlist on PANDAS, NUMPY please🌸
🌺🌼

[@Prateek_Mantry]

Hi Bro....Please make more videos.

[@Delicatamente]

So, technicaly, timer re-renders every 10 miliseconds, just because of changing useState variable "elapsedTime" in Stopwatch component, what provide full re-render of Stopwatch component?
Or re-render happens as a result of changing that useState variable "elapsedTime", which is mentioned in function "formatTime", which (this function) is mapped to timer component? And because of this bound React re-renders component?
Can someone explain me this technical details?

[@1CDzy]

bro, please do C# on NET. development

[@astartesidon609]

so we can conclude that even if we stop the countdown for a couple of minutes still the time in between when we restart still gonna carry over because we based our elapsed time only on a date?

[@yogii1108]

bro start next js using JavaScript waiting to learn from your channel

[@ranjithkumar7896]

Bro continue the react series, enjoying it try to upload next videos faster

[@cobragaming-jv7iz]

Baga cheppara bro

[@tasfin660]

I want more react videos

[@arkartm9989]

True Chad bro..❤

[@ejebeueh9113]

Bro please i need help I just started learning jave script and I'm watching your full course so when I linked my css ,js and HTML and tried the same code that you wrote and opened it with live server nothing appeared on the web and its console it says error404
Sorry for my poor words
I hope that you understand what I mean, thanks

[@aman1589]

did u install live server?

[@its-SK]

hey bro code I am facing difficulties while learning js what should i do?

[@1CDzy]

look at the documentation on JS, maybe it will help

[@anandv1391]

Mbuf

[@RealRower1]

hey Bro Code can you make a course about lua

[@RealRower1]

ye but atleast he has something to post about and i think he is gonna get alot of views because lot of people want to learn lua for game dev in roblox and there is not a good course to learning it so he will be the first

[@ACCOUNT72197]

Hey i just wanted to say your last 5 videos don't appear in my sub feed. What is going on

[@BishanTamang-rk5ji]

Make java 2024 plz bro code love from Nepal 💓💓

[@_amonimus_]

bro how many languages do you know

[@jacklagos936]

Bring parallax plz

[@Beanbag59]

Do u tutor

[@reynaldobuscagan7731]

Hello, I'm a beginner I wonder what app you use, is it html or eclipse?

[@yaroslavluchko8492]

this is VSCode