cringe-studios.com/special/new-year.js

const EXPLOSION_TIME = 100;
const EXPLOSION_SIZE = 100;
const NUM_PARTICLES = 12;
const SPEED = 2;
let OVERRIDE_STATE = null;

function HSVtoRGB(h, s, v) {
	var r, g, b, i, f, p, q, t;
	if (arguments.length === 1) {
		s = h.s, v = h.v, h = h.h;
	}
	i = Math.floor(h * 6);
	f = h * 6 - i;
	p = v * (1 - s);
	q = v * (1 - f * s);
	t = v * (1 - (1 - f) * s);
	switch (i % 6) {
		case 0: r = v, g = t, b = p; break;
		case 1: r = q, g = v, b = p; break;
		case 2: r = p, g = v, b = t; break;
		case 3: r = p, g = q, b = v; break;
		case 4: r = t, g = p, b = v; break;
		case 5: r = v, g = p, b = q; break;
	}

	return "rgb(" + (r * 255) + "," + (g * 255) + "," + (b * 255) + ")";
}

const canvas = document.getElementById("fireworks-canvas");
const updateSize = () => {
	canvas.width = window.innerWidth;
	canvas.height = window.innerHeight;
};

const STATE_NONE = "NONE";
const STATE_COUNTDOWN = "COUNTDOWN";
const STATE_FIREWORKS = "FIREWORKS";

let rockets = [];
let state = STATE_NONE;

updateSize();
window.onresize = updateSize;

const ctx = canvas.getContext("2d");

function leftPad(str, len, pad) {
	str = "" + str;

	while (str.length < len) {
		str = pad + str;
	}

	return str;
}

window.addEventListener("keyup", e => {
	if (e.key == 'h') {
		canvas.style.display = canvas.style.display == 'none' ? null : 'none';
	}
});

setInterval(() => {
	const theTime = new Date();

	if (OVERRIDE_STATE != null) {
		state = OVERRIDE_STATE;
	} else if (theTime.getDate() == 1 && theTime.getMonth() == 0 && theTime.getHours() == 0) { // 01.01. 00:00 - 00:59
		state = STATE_FIREWORKS;
	} else {
		const nextYear = new Date('1970-01-01 00:00');
		nextYear.setFullYear(theTime.getFullYear() + 1);
		const timeUntilMidnight = Math.floor((nextYear - theTime) / 1000);

		if(timeUntilMidnight < 4 * 60 * 60) {
			state = STATE_COUNTDOWN;
		}else {
			state = STATE_NONE;
		}
	}

	if (state == STATE_FIREWORKS) {
		rockets.push({ x: Math.random() * canvas.width, y: canvas.height, life: (Math.random() * 0.75 + 0.25) * canvas.height, color: HSVtoRGB(Math.random(), 1, 1) });
		return;
	} else {
		rockets = [];
	}
}, 300);

setInterval(() => {
	if (state == STATE_NONE) {
		ctx.clearRect(0, 0, canvas.width, canvas.height);
		return;
	}

	const theTime = new Date();

	switch (state) {
		case STATE_NONE:
			ctx.clearRect(0, 0, canvas.width, canvas.height);
			return;
		case STATE_COUNTDOWN:
			ctx.fillStyle = "#000044ff";
			ctx.fillRect(0, 0, canvas.width, canvas.height);

			const nextYear = new Date('1970-01-01 00:00');
			nextYear.setFullYear(theTime.getFullYear() + 1);
			const timeUntilMidnight = Math.floor((nextYear - theTime) / 1000);
			const hours = "" + Math.floor(timeUntilMidnight / (60 * 60));
			const minutes = "" + Math.floor((timeUntilMidnight / 60) % 60);
			const seconds = "" + Math.floor(timeUntilMidnight % 60);

			ctx.fillStyle = "orangered";
			ctx.textAlign = "center";
			ctx.font = "bold 50px Comic Mono";
			ctx.fillText("T - " + hours.padStart(2, "0") + ":" + minutes.padStart(2, "0") + ":" + seconds.padStart(2, "0"), canvas.width / 2, canvas.height / 2);

			ctx.fillStyle = "white";
			ctx.fillText(theTime.getHours().toString().padStart(2, '0') + ":" + theTime.getMinutes().toString().padStart(2, '0') + ":" + theTime.getSeconds().toString().padStart(2, '0'), canvas.width / 2, canvas.height / 2 - 150);

			ctx.fillStyle = "lightgray";
			ctx.textAlign = "center";
			ctx.font = "bold 30px Comic Mono";

			let text = "The new year is approaching 👀";
			if(hours < 1) {
				text = "The final hour has started ⏱️";

				if(minutes == 0 && seconds < 60) {
					text = "It's the final countdown 😳"
				}
			}

			ctx.fillText(text, canvas.width / 2, canvas.height / 2 + 150);
			break; // Draw help
		case STATE_FIREWORKS:
			ctx.fillStyle = "#000044ff";
			ctx.fillRect(0, 0, canvas.width, canvas.height);

			rockets.forEach(rocket => {
				rocket.life -= SPEED;

				if (rocket.life <= EXPLOSION_TIME) {
					if (rocket.life <= 0) {
						rockets.splice(rockets.indexOf(rocket), 1);
						return;
					}

					const explosionTime = 1 - (rocket.life / EXPLOSION_TIME);
					const size = explosionTime * EXPLOSION_SIZE;

					for (let i = 0; i < NUM_PARTICLES; i++) {
						const angle = i / NUM_PARTICLES * Math.PI * 2;
						const px = Math.cos(angle) * size;
						const py = Math.sin(angle) * size;

						ctx.fillStyle = rocket.color;
						ctx.beginPath();
						ctx.arc(rocket.x + px, rocket.y + py, 5, 0, Math.PI * 2, true);
						ctx.fill();
					}
				} else {
					rocket.y -= SPEED;
					ctx.fillStyle = "black";
					ctx.fillRect(rocket.x - 5, rocket.y - 5, 10, 10);
				}

			});

			ctx.fillStyle = "white";
			ctx.textAlign = "center";
			ctx.font = "bold 50px Comic Mono";
			ctx.fillText("Happy new year! 🥳", canvas.width / 2, canvas.height / 2);
			ctx.font = "bold 100px Comic Mono";
			ctx.fillText(theTime.getHours().toString().padStart(2, '0') + ":" + theTime.getMinutes().toString().padStart(2, '0') + ":" + theTime.getSeconds().toString().padStart(2, '0'), canvas.width / 2, canvas.height / 2 - 150);
			break; // Draw help
	}

	ctx.font = "bold 10px Comic Mono";
	ctx.fillStyle = "#0000ff";
	ctx.textAlign = "left";
	ctx.fillText("Press 'h' to hide", 10, canvas.height - 10);
}, 10);