smoothScroll.js

function sleep(ms) {
	return new Promise(resolve => setTimeout(resolve, ms));
}

async function smoothScrollToTop(elemId) {
	const speed = 1000; //ms
	let targetY = document.querySelector(`#${elemId}`).offsetTop;
	let curPos = window.scrollY;
	let steps = 100;

	let calcPixelStep = (targetY - curPos)/steps;
	let timeDelay = speed/steps;

	let actualPixelStep = Math.floor(calcPixelStep);
	let remainder = (targetY - curPos) - (actualPixelStep * steps)
	console.log(actualPixelStep, remainder);

	for(let i = 0; i <= steps; i++) {
		window.scrollBy(0,actualPixelStep);
		await sleep(timeDelay);
	}
	window.scrollBy(0,remainder);
}