TimeAgo - ES6

timeago.js

// Epochs
const epochs = [
    ['year', 31536000],
    ['month', 2592000],
    ['day', 86400],
    ['hour', 3600],
    ['minute', 60],
    ['second', 1]
];


// Get duration
const getDuration = (timeAgoInSeconds) => {
    for (let [name, seconds] of epochs) {
        const interval = Math.floor(timeAgoInSeconds / seconds);

        if (interval >= 1) {
            return {
                interval: interval,
                epoch: name
            };
        }
    }
};


// Calculate
const timeAgo = (date) => {
    const timeAgoInSeconds = Math.floor((new Date() - new Date(date)) / 1000);
    const {interval, epoch} = getDuration(timeAgoInSeconds);
    const suffix = interval === 1 ? '' : 's';

    return `${interval} ${epoch}${suffix} ago`;
};

Updated epochs to an array because the sequence of the values is important. Properties order in objects is not guaranteed in JavaScript. Kudos to @pjaspers for pointing this one out!