Instead of Moment.js: date-fns

Why date-fns is better

• Moment objects are mutable, so adding a day to one changes it everywhere it is shared. date-fns functions are pure and always return a new Date.
• You import only the functions you use and bundlers drop the rest. Moment's minified file is 19.1k without locales and 77.4k with them, and it has no native ES module entry point.
• It works on the built-in Date type instead of a wrapper object, so values pass to other libraries and APIs unchanged.
• It is written in TypeScript with handcrafted types, and you load only the locales you need.
• Version 4 added first-class time zone support, which Moment needs the separate Moment Timezone package for.

When to keep Moment.js

Keep Moment in an older app that works and rarely changes, since maintenance mode still brings fixes, though no new features. Date code is easy to break, so replacing Moment file by file as you touch it is safer than one large pass.

Switching

Each call site gets rewritten. moment(x).add(1, 'days').format('YYYY-MM-DD') becomes format(addDays(x, 1), 'yyyy-MM-dd'). The format tokens differ too, since date-fns uses Unicode tokens where Moment uses its own, so check every format string. Day.js keeps most of Moment's API and tokens, which makes it the quicker swap for a large codebase.

Watch out

date-fns still uses JavaScript's Date, which has no separate type for a plain calendar date or a wall-clock time, so time zone mistakes remain possible. Temporal fixes that at the language level, but MDN still marks it as limited availability because it does not work in some widely used browsers. Once it does, many projects will need no date library at all.

Also worth a look

• Day.js A 2kB library with a largely Moment-compatible chained API and immutable objects; pick it to migrate a big Moment codebase with the fewest call-site changes.
• Temporal The built-in replacement for JavaScript's Date, with separate types for dates, times and zoned date-times; use it where your runtimes support it, or through a polyfill.

More newer, better libraries, runtimes and developer tools

• Lodash →, use es-toolkit
• Axios →, use Ky
• Redux →, use Zustand
• styled-components →, use Tailwind CSS
• Prisma ORM →, use Drizzle ORM
• ImageMagick →, use libvips
• Beautiful Soup →, use selectolax