Twitter style relative time.

relative-time.js

const computeRelativeTime = (time) => {
	if(typeof time === 'string') {
		return computeRelativeTime(new Date(time));
	}

	const plural = (val) => val !== 1 ? 's' : '';
	const format = (val, unit) => `${val} ${unit}${plural(val)} ago`;

	let diff = (Date.now() - time.getTime()) / 1000;

	if (diff<60) {
		return format(diff, 'second');
	}

	diff = Math.round(diff/60);
	if (diff<60) {
		return format(diff, 'minute');
	}

	diff = Math.round(diff/60);
	if (diff<24){
		return format(diff, 'hour');
	}

	diff = Math.round(diff/24);
	if (diff<7){
		return format(diff, 'day');
	}

	diff = Math.round(diff/7);
	if (diff<4){
		return format(diff, 'week');
	}

	return `on ${time.toLocaleDateString('en-US', { year: 'numeric', month: 'long', day: 'numeric' })}`;
}

relative-time.ts

const computeRelativeTime = (time: string | Date): string => {
	if(typeof time === 'string') {
		return computeRelativeTime(new Date(time));
	}

	const plural = (val: number) => val !== 1 ? 's' : '';
	const format = (val: number, unit: string) => `${val} ${unit}${plural(val)} ago`;

	let diff = (Date.now() - time.getTime()) / 1000;

	if (diff<60) {
		return format(diff, 'second');
	}

	diff = Math.round(diff/60);
	if (diff<60) {
		return format(diff, 'minute');
	}

	diff = Math.round(diff/60);
	if (diff<24){
		return format(diff, 'hour');
	}

	diff = Math.round(diff/24);
	if (diff<7){
		return format(diff, 'day');
	}

	diff = Math.round(diff/7);
	if (diff<4){
		return format(diff, 'week');
	}

	return `on ${time.toLocaleDateString('en-US', { year: 'numeric', month: 'long', day: 'numeric' })}`;
}