Moment-compatible migration bridge
mmntjs is a compatibility-first replacement for teams that cannot justify a risky date/time rewrite today, but still want a smaller, better-tested path forward.
Recommended: lite (55.2KB raw bundled, moment-compatible)
import moment from "mmntjs/lite";
moment()
.add(1, "day")
.format("YYYY-MM-DD");Also available: fns (standalone functions)
import {
format,
startOf,
add,
} from "mmntjs/fns";
format(
add(new Date(), 1, "day"),
"YYYY-MM-DD",
);Full: moment.js compat (179.5KB raw bundled)
import moment from "mmntjs";
moment
.utc("2024-01-01")
.format("YYYY-MM-DD");Migration tool
# analyze usage
mmntjs migrate --check
# npm alias, zero code change
mmntjs migrate --mode=alias
# auto-choose best target
mmntjs migrate --apply
# force fns
mmntjs migrate --apply --fnsThe hard truth
Date/time rewrites rarely fail in the obvious paths. They fail in parsing edge cases, invalid-date handling, DST transitions, offsets, and locale behavior that production code has quietly depended on for years.
Quick Start
Evaluate mmntjs in one module, run the tests you already trust, and expand only after checking compatibility-sensitive behavior.
# recommended: lite
# 55.2KB raw bundled, moment-compatible
npm install mmntjs
import moment from "mmntjs/lite";
moment()
.add(1, "day")
.format("YYYY-MM-DD");
# or standalone functions (small base)
import {
format,
add,
} from "mmntjs/fns";
# or full compat for migration
# 179.5KB raw bundled
import moment from "mmntjs";
moment
.utc("2024-01-01")
.format();Why mmntjs
630/630 moment.js 2.30.1 tests pass, verified by oracle tests and fuzzing. The mmntjs CLI automates import rewrites and generates migration reports.
A modern TypeScript implementation that is both smaller than moment.js and faster on every tracked operation, without sacrificing compatibility.
Adopt incrementally today, then move new code toward Temporal over time rather than via a forced rewrite.
Compatibility Snapshot
| Area | Status | Notes |
|---|---|---|
| Formatting | Compatible | Token and locale output are covered by upstream and locale-derived tests. |
| Manipulation | Compatible | add/subtract/startOf/endOf semantics are treated as compatibility-critical. |
| Query and comparison | Compatible | diff and comparison methods are covered by oracle and property tests. |
| Duration | Compatible | Construction, normalization, and relative-time behavior are part of the test matrix. |
| Locale | Compatible | Locale behavior is validated against the upstream locale suite. |
| UTC and parseZone | Compatible | UTC and fixed-offset behavior are tested; timezone package provides compatible IANA timezone data support. |
| Invalid dates | Compatible | Examples: moment("2024-02-31"), moment("not-a-date"), moment([2024, 1, 31]), and moment.invalid(). |
| Parsing | Mostly compatible | Standard ISO, RFC 2822, custom format, array, object, sign-prefixed, and control-character inputs match moment.js. One known difference is mixed input like "93280531 09-3911". |
Quality
Performance
Migration Path
Inventory current moment usage with mmntjs migrate --check. Identify timezone, locale, and parsing hotspots.
Optionally set npm alias with mmntjs migrate --mode=alias: zero code change, lets your build tool resolve moment → mmntjs at install time.
Run mmntjs migrate --apply to auto-rewrite imports. For full-only codebases, start with mmntjs (full compat). For lite-compatible code, switch directly to mmntjs/lite.
If your code only uses basic formatting/manipulation, mmntjs/fns is an option: standalone functions with tree-shakeable cost. Run mmntjs migrate --apply --fns --dry to preview.
Run compatibility checks and review known differences for the APIs your codebase uses. Compare production-like behavior, especially invalid dates, offsets, and custom parsing.
Replace imports in a low-risk module or service and run the existing test suite. Expand rollout module by module with ownership and rollback clarity.
Use the bridge period to guide new code toward modern date/time APIs, including Temporal where it fits.
FAQ
Docs