Dates and times are incredibly complex. They can be different in different countries, languages. They are often inconsistent and have weird edge-cases. These are some basic rules I apply when working with dates and times.

<p>when handling dates and timestamps, here are the foundation rules that I work to:</p> <ul> <li> <p><strong>Always use ISO date format where possible</strong> (YYYY-MM-DD)</p> <p>So that there can be no ambiguity and so that date strings will naturally sort</p> </li> <li> <p><strong>Always work in UTC</strong> (Aka Zulu time or GMT) except when displaying to the user</p> <p>To avoid weird errors, especially with timezone and daylight savings transitions. It also makes date/time calculations a LOT easier.</p> </li> <li> <p><strong>When needing a string format for timestamps, always use ISO format</strong></p> <p>e.g. <code>2020-03-07T15:27:46.123Z</code></p> <p>These are always unambiguous and easily machine parsed.</p> </li> <li> <p><strong>When specifying decimal seconds in a timestamp, avoid more than 3 decimal places</strong></p> <p>The <a href="https://github.com/gr2m/moment-parseformat">parsing tool</a> used in <a href="">node-red-contrib-moment</a> to parse input dates in different formats cannot cope with more than 3dp and may return strange dates, a problem that I reported in May 2019 but hasn&rsquo;t been resolved.</p> <p>It should also be noted that I&rsquo;m not sure that MomentJS can cope with more than 9dp.</p> <p>Also worth noting that JavaScript&rsquo;s <code>Date</code> native object only supports up to 3dp anyway and will turn anything beyond that into zero&rsquo;s.</p> </li> </ul> <h2 id="references">References</h2> <ul> <li> <p><a href="https://github.com/gr2m/moment-parseformat/issues/96">parseFormat function issue for &gt;3dp seconds resolution</a></p> <p>The worst thing about this issue is that it can result in an incorrect date being returned but does not give a warning.</p> </li> </ul>