vanilla-lazyload/src/lazyload.class.js

A fast, lightweight script to load images as they enter the viewport. SEO friendly, it supports responsive images (both srcset + sizes and picture) and progressive JPEG

import { supportsClassList } from "./lazyload.environment";

export const addClass = (element, className) => {
	if (supportsClassList) {
		element.classList.add(className);
		return;
	}
	element.className += (element.className ? " " : "") + className;
};

export const removeClass = (element, className) => {
	if (supportsClassList) {
		element.classList.remove(className);
		return;
	}
	element.className = element.className.
		replace(new RegExp("(^|\\s+)" + className + "(\\s+|$)"), " ").
		replace(/^\s+/, "").
		replace(/\s+$/, "");
};