Countdown Timer in JavaScript

1// Method 1: Simple countdown
2function countdown(targetDate, callback) {
3    const interval = setInterval(() => {
4        const now = new Date().getTime();
5        const distance = targetDate.getTime() - now;
6        
7        if (distance < 0) {
8            clearInterval(interval);
9            callback({ expired: true });
10            return;
11        }
12        
13        const days = Math.floor(distance / (1000 * 60 * 60 * 24));
14        const hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
15        const minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
16        const seconds = Math.floor((distance % (1000 * 60)) / 1000);
17        
18        callback({
19            days,
20            hours,
21            minutes,
22            seconds,
23            total: distance
24        });
25    }, 1000);
26}
27
28const target = new Date(Date.now() + 86400000); // 1 day from now
29countdown(target, (time) => {
30    if (time.expired) {
31        console.log('Countdown expired!');
32    } else {
33        console.log(`${time.days}d ${time.hours}h ${time.minutes}m ${time.seconds}s`);
34    }
35});
36
37// Method 2: Countdown class
38class CountdownTimer {
39    constructor(targetDate, onUpdate, onComplete) {
40        this.targetDate = targetDate;
41        this.onUpdate = onUpdate;
42        this.onComplete = onComplete;
43        this.interval = null;
44    }
45    
46    start() {
47        this.update();
48        this.interval = setInterval(() => this.update(), 1000);
49    }
50    
51    stop() {
52        if (this.interval) {
53            clearInterval(this.interval);
54            this.interval = null;
55        }
56    }
57    
58    update() {
59        const now = new Date().getTime();
60        const distance = this.targetDate.getTime() - now;
61        
62        if (distance < 0) {
63            this.stop();
64            if (this.onComplete) this.onComplete();
65            return;
66        }
67        
68        const time = {
69            days: Math.floor(distance / (1000 * 60 * 60 * 24)),
70            hours: Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60)),
71            minutes: Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60)),
72            seconds: Math.floor((distance % (1000 * 60)) / 1000),
73            total: distance
74        };
75        
76        if (this.onUpdate) this.onUpdate(time);
77    }
78    
79    getRemaining() {
80        const now = new Date().getTime();
81        const distance = this.targetDate.getTime() - now;
82        return distance > 0 ? distance : 0;
83    }
84}
85
86const timer = new CountdownTimer(
87    new Date(Date.now() + 3600000), // 1 hour
88    (time) => console.log(`${time.minutes}m ${time.seconds}s`),
89    () => console.log('Timer complete!')
90);
91timer.start();