Lokely使用的一个简短版本:

const intervals = [
  { label: 'year', seconds: 31536000 },
  { label: 'month', seconds: 2592000 },
  { label: 'day', seconds: 86400 },
  { label: 'hour', seconds: 3600 },
  { label: 'minute', seconds: 60 },
  { label: 'second', seconds: 1 }
];

function timeSince(date) {
  const seconds = Math.floor((Date.now() - date.getTime()) / 1000);
  const interval = intervals.find(i => i.seconds < seconds);
  const count = Math.floor(seconds / interval.seconds);
  return `${count} ${interval.label}${count !== 1 ? 's' : ''} ago`;
}

我还没有检查(虽然这并不难)，但我认为Stack Exchange站点使用jquery。Timeago插件来创建这些时间字符串。

这个插件使用起来很简单，而且很干净，还能自动更新。

下面是一个简单的例子(来自插件的主页):

First, load jQuery and the plugin: <script src="jquery.min.js" type="text/javascript"></script> <script src="jquery.timeago.js" type="text/javascript"></script> Now, let's attach it to your timestamps on DOM ready: jQuery(document).ready(function() { jQuery("abbr.timeago").timeago(); }); This will turn all abbr elements with a class of timeago and an ISO 8601 timestamp in the title: <abbr class="timeago" title="2008-07-17T09:24:17Z">July 17, 2008</abbr> into something like this: <abbr class="timeago" title="July 17, 2008">about a year ago</abbr> which yields: about a year ago. As time passes, the timestamps will automatically update.

function calDateAgo(dString=null){
    //var dString = "2021-04-1 12:00:00";
     
    var d1 = new Date(dString);
    var d2 = new Date();
    var t2 = d2.getTime();
    var t1 = d1.getTime();
    var d1Y = d1.getFullYear();
    var d2Y = d2.getFullYear();
    var d1M = d1.getMonth();
    var d2M = d2.getMonth();
     
    var time_obj = {};
    time_obj.year = d2.getFullYear()-d1.getFullYear();
    time_obj.month = (d2M+12*d2Y)-(d1M+12*d1Y);
    time_obj.week = parseInt((t2-t1)/(24*3600*1000*7));
    time_obj.day = parseInt((t2-t1)/(24*3600*1000));
    time_obj.hour = parseInt((t2-t1)/(3600*1000));
    time_obj.minute = parseInt((t2-t1)/(60*1000));
    time_obj.second = parseInt((t2-t1)/(1000));

    for (const obj_key in time_obj) {
        if(time_obj[obj_key] == 0){
            delete time_obj[obj_key];
        }
    }
    var ago_text = 'just now';

    if(typeof Object.keys(time_obj)[0] != 'undefined'){
        var time_key = Object.keys(time_obj)[0];
        var time_val = time_obj[Object.keys(time_obj)[0]];
        time_key += (time_val > 1) ? 's':'';
        ago_text = time_val+' '+time_key+' ago'; 
    }
    
    return ago_text;
}

我的解决方案。

(function(global){
            const SECOND   = 1;
            const MINUTE   = 60;
            const HOUR     = 3600;
            const DAY      = 86400;
            const MONTH    = 2629746;
            const YEAR     = 31556952;
            const DECADE   = 315569520;

            global.timeAgo = function(date){
                var now = new Date();
                var diff = Math.round(( now - date ) / 1000);

                var unit = '';
                var num = 0;
                var plural = false;

                switch(true){
                    case diff <= 0:
                        return 'just now';
                    break;

                    case diff < MINUTE:
                        num = Math.round(diff / SECOND);
                        unit = 'sec';
                        plural = num > 1;
                    break;

                    case diff < HOUR:
                        num = Math.round(diff / MINUTE);
                        unit = 'min';
                        plural = num > 1;
                    break;

                    case diff < DAY:
                        num = Math.round(diff / HOUR);
                        unit = 'hour';
                        plural = num > 1;
                    break;

                    case diff < MONTH:
                        num = Math.round(diff / DAY);
                        unit = 'day';
                        plural = num > 1;
                    break;

                    case diff < YEAR:
                        num = Math.round(diff / MONTH);
                        unit = 'month';
                        plural = num > 1;
                    break;

                    case diff < DECADE:
                        num = Math.round(diff / YEAR);
                        unit = 'year';
                        plural = num > 1;
                    break;

                    default:
                        num = Math.round(diff / YEAR);
                        unit = 'year';
                        plural = num > 1;
                }

                var str = '';
                if(num){
                    str += `${num} `;
                }

                str += `${unit}`;

                if(plural){
                    str += 's';
                }

                str += ' ago';

                return str;
            }
        })(window);

        console.log(timeAgo(new Date()));
        console.log(timeAgo(new Date('Jun 03 2018 15:12:19 GMT+0300 (FLE Daylight Time)')));
        console.log(timeAgo(new Date('Jun 03 2018 13:12:19 GMT+0300 (FLE Daylight Time)')));
        console.log(timeAgo(new Date('May 28 2018 13:12:19 GMT+0300 (FLE Daylight Time)')));
        console.log(timeAgo(new Date('May 28 2017 13:12:19 GMT+0300 (FLE Daylight Time)')));
        console.log(timeAgo(new Date('May 28 2000 13:12:19 GMT+0300 (FLE Daylight Time)')));
        console.log(timeAgo(new Date('Sep 10 1994 13:12:19 GMT+0300 (FLE Daylight Time)')));

Lokely使用的一个简短版本:

const intervals = [
  { label: 'year', seconds: 31536000 },
  { label: 'month', seconds: 2592000 },
  { label: 'day', seconds: 86400 },
  { label: 'hour', seconds: 3600 },
  { label: 'minute', seconds: 60 },
  { label: 'second', seconds: 1 }
];

function timeSince(date) {
  const seconds = Math.floor((Date.now() - date.getTime()) / 1000);
  const interval = intervals.find(i => i.seconds < seconds);
  const count = Math.floor(seconds / interval.seconds);
  return `${count} ${interval.label}${count !== 1 ? 's' : ''} ago`;
}

简单易读版本:

const relativeTimePeriods = [
    [31536000, 'year'],
    [2419200, 'month'],
    [604800, 'week'],
    [86400, 'day'],
    [3600, 'hour'],
    [60, 'minute'],
    [1, 'second']
];

function relativeTime(date, isUtc=true) {
    if (!(date instanceof Date)) date = new Date(date * 1000);
    const seconds = (new Date() - date) / 1000;
    for (let [secondsPer, name] of relativeTimePeriods) {
        if (seconds >= secondsPer) {
            const amount = Math.floor(seconds / secondsPer);
            return `${amount} ${name}${amount ? 's' : ''}s ago`;
        }
    }
    return 'Just now';
}