flashing.js

const COLORS = ["#fff42d", "#f909dd", "#FD5F00"];
const IMAGES = ["/images/lechickens.png", "/images/lechickens2.png", "/images/lechickens3.png"];
const FLASH_DELAY = 50; // milliseconds between flashes

let _nextColor = 0;
let _nextImage = 0;

function initFlashing() {
	_loadImage(0);
	setInterval(_flashBodyBackground, FLASH_DELAY);
}

function _loadImage(num) {
	if (!(0 <= num && num < IMAGES.length)) return;
	let dlImage = new Image();
	dlImage.onload = function () {
		document.getElementById("img-load-area").innerHTML += "<img src=\"" + this.src + "\" />";
		_loadImage(num+1);
	}
	dlImage.src = IMAGES[num];
}

function _flashBodyBackground() {
	document.getElementsByTagName("body")[0].style.backgroundColor = COLORS[_nextColor];
	document.getElementsByTagName("body")[0].style.backgroundImage = "url('" + IMAGES[_nextImage] + "')";
	_nextColor++; _nextColor %= COLORS.length;
	_nextImage++; _nextImage %= IMAGES.length;
}