A guide to hiring a Moment.js developer
Moment.js is a JavaScript library for working with dates and times. Many apps, dashboards and booking tools were built with it, and a lot of that code is still running. A Moment.js developer keeps this code correct and, when it makes sense, helps move it to something newer. This guide explains what the work involves, when you need it and how to choose well. It is written for founders, product owners and engineering leads whose apps show the wrong date, or who wonder what to do with an old date library.
What a Moment.js developer is responsible for
This developer owns everything in your code that touches dates and times. That includes reading dates from forms and APIs, saving them safely, showing them in the right format and zone, and calculating things like deadlines, renewals and reports by week. They find the places where a date can shift by a day, write tests for them and leave notes so the next person understands the rules. On a bigger project they also plan how to retire an old library without risking the product.
Why date code goes wrong
People think of a date as one thing, but code has to treat it in several ways. It might be a point in time, a day on a calendar, a length of time or a repeating event. Add time zones, daylight saving and different languages, and small mistakes multiply. A customer may see a booking on the wrong day, or a report may skip an hour. These bugs are hard to spot because they only appear for some users, on some days. Experience matters more than speed here.
About Moment.js today
Moment.js has been a common choice for years, so you will find it in many older projects. The Moment.js project describes itself as a legacy project in maintenance mode, and its team suggests other libraries for new work. That does not mean your app is broken. It means you should decide on purpose whether to keep it, and plan any move with care. A good developer helps you weigh the cost of staying against the cost of changing.
How this role differs from nearby roles
A JavaScript developer covers the whole front end and often the server, so choose that page when dates are only part of a bigger job. A Node.js developer works on the server side, where many date calculations also run. An Angular developer or a React developer builds the screens that show the dates. Use the Moment.js page when the dates themselves are the issue.
When a Moment.js developer makes sense
- Users report the wrong date, or a time that is off by an hour.
- Your customers live in several countries and see mismatched times.
- Your app uses Moment.js and nobody on the team knows it well.
- You want to plan a move to a newer date library without a risky rewrite.
- You need reports, bookings or reminders that stay correct across clock changes.
If dates are a small part of your app and nothing is broken, a general developer may be enough.
What to look for in a background
Ask for examples where the person fixed a real date problem. A good answer says what users saw, what caused it and how it was tested. Be careful with a person who says that dates are easy. Ask them to explain, in simple words, why an event in the early morning can be a problem on the day the clocks change.
Interview questions to try
- How do you store a meeting time so it shows correctly for people in different countries?
- What can go wrong when you change a Moment object, and how do you avoid it?
- How would you test a function that depends on the current date?
- How would you move one screen from Moment to a newer library without changing what users see?
- What would you check first if a report is one day off for some users only?
Look for calm, specific answers with an example behind each one. Be cautious with answers that skip over time zones.
A paid trial task
Pick a real date feature from your app, such as a booking form or a weekly report. Ask each finalist to review it, list the risks and fix one bug with a test. Pay for the time. You will learn how they think, how well they test and how clearly they explain a hard topic to a person outside engineering.
Match the person to the job
A product with users in many countries needs someone strong on time zones and languages. An older app with a lot of Moment code needs a patient reader who plans a move in small steps. A new product needs advice on which library to start with. Ask each candidate which of these they have done before.
Access and routine
Decide the weekly hours up front and revisit them now and then. Give your engineer personal logins to the code host and the test site, and keep every account in the company name. Ask for a note on each change explaining how to roll it back. Close the access on the last day of the work.
Working with the rest of your team
Share a list of the screens and reports that show dates, and tell the team which rules the business depends on, such as which time zone a deadline uses. Set one team rule for how dates are stored and shown, and write it down. A short weekly review of open changes keeps things on track.
Mistakes to avoid
- Testing dates only on the developer’s own computer and in a single time zone.
- Saving local times with no zone, then trying to guess the zone later.
- Switching libraries across the whole app in a single release.
- Leaving two date libraries in place with no plan to remove one.
Need help beyond dates? See our JavaScript developers, or read about our Node.js developers if the work runs on the server.