Building a JavaScript Relationship Duration Calculator — How Would You Improve It?

Hello everyone,

I’ve been exploring how simple web applications can turn everyday calculations into something useful and interactive.

One example is a relationship duration calculator that takes a starting date and calculates the time elapsed in days, hours, minutes, and seconds. The idea is straightforward, but implementing it raises some interesting technical questions about date handling, real-time updates, and user experience.

For anyone interested in seeing how this type of online date calculator.

I’m particularly interested in the engineering side of these small web applications:

• Would you use JavaScript's built-in Date object or a dedicated date-time library?

• How would you handle timezone differences and daylight saving changes?

• Is it better to update the displayed duration every second or calculate it only when the user opens the page?

• What approaches would you recommend for keeping a lightweight web calculator responsive on mobile devices?

I’d love to hear how other developers would approach the design and implementation of a simple date-based web application.