JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://rawgit.com/slevithan/xregexp/master/xregexp-all.js"></script>

JavaScript

var testStr1 = '15:05  up 1 day, 10:40, 4 users, load averages: 1.68 1.30 1.30';
var testStr2 = '12:27:57 up 25 min,  load average: 0.33, 0.33, 0.28';
var testStr3 = '12:27:58 up  1:26,  load average: 5.44, 5.29, 5.26';
var testStr4 = '00:36:55 up 16 days, 26 min,  load average: 0.83, 0.75, 0.76';

var uptimeRegex = XRegExp('(?<timeHour>\d{1,2}):(?<timeMinute>\d{2})(?:\:(?<timeSecond>\d{2}))?\s+up\s+(?:(?<upDays>\d+)\s+days?,\s+)?\b(?:(?<upHours>\d+):)?(?<upMinutes>\d+)(?:\s+min?)?,\s+.+?(?<load1>\d+\.\d+),?\s+(?<load2>\d+\.\d+),?\s+(?<load3>\d+\.\d+)');

var test1 = uptimeRegex.test(testStr1);
var test2 = uptimeRegex.test(testStr2);
var test3 = uptimeRegex.test(testStr3);
var test4 = uptimeRegex.test(testStr4);

results =  test1 + ' ' + test2 + ' ' + test3 + ' ' + test4;
document.body.innerText = results;