Restore a scroll position after a content change

scrollPosition.js

import passive from './setPassiveEvent.js';

// DOMMouseScroll is specific to Firefox
const eventTypes = ['mousewheel', 'touchmove', 'DOMMouseScroll'];

class ScrollPosition {

	constructor(viewport) {
		this.viewport = viewport || document.body;
		this.scrollPosition = this.getScrollPosition();
		this.listenerMethod = 'add';
	}

	handleEvent() {
		this.scrollPosition = this.getScrollPosition();
	}

	getScrollPosition() {
		return { left: this.viewport.scrollLeft, top: this.viewport.scrollTop };
	}
	setScrollPosition() {
		scrollTo(this.scrollPosition.left, this.scrollPosition.top);
		this.listenerMethod = 'remove';
	}

	set listenerMethod(prefix) {
		eventTypes.forEach(type => {
			this.viewport[`${prefix}EventListener`](type, this, passive);
		});
	}

}

export default function(viewport) {
	if ('addEventListener' in window) {
		return new ScrollPosition(viewport);
	}
}