Main point
The default mmntjs entry is not trying to win the smallest-core contest.
mmntjs
Compatibility-first migration bridge away from moment.js
Package Size
Package size is not one number.
Measure raw, minified, compressed, bundled, and runtime costs separately. `mmntjs` default is compatibility-heavy, so the raw core is not the main selling point. The more important property is that locale data and timezone data are kept separate, which gives tree-shaking and entry-point choice real leverage.
What To Understand
What it does win
Locales and timezone data are separate, so apps do not pay for them unless they import them.
Lite entry
mmntjs/lite exists for browser-sensitive paths that want a smaller base and explicit add-backs.
Timezone surprise
The packaged IANA timezone data is smaller than many readers expect once compressed and packed.
Entry Sizes
Compare each entry against the moment.js shape it replaces.
| Entry | Raw size | Compare against | Reading | Why it matters |
|---|---|---|---|---|
mmntjs | 148 KB | moment (62.1 KB raw) | core is smaller on the moment side | Default compatibility-oriented core. |
mmntjs/lite | 43 KB | moment (62.1 KB raw) | smaller base than moment and default mmntjs | Browser-sensitive base entry with explicit add-backs. |
dist/locale/ja.js | 4.8 KB | moment + locale/ja (64.5 KB raw bundled) | single locale stays separate | Single locale remains a tiny extra module instead of pushing toward all-locales builds. |
mmntjs-timezone | 316 KB raw dist | moment-timezone (773.1 KB raw bundled) | compare as separate package | Timezone data stays outside core and should be judged on its own. |
Why This Helps
- Moment's common browser story often drifts toward larger all-locales or timezone-heavy builds.
- mmntjs keeps the compatibility-heavy core separate from locale data and timezone data. As a follow-up to that design, it is also easier to tree-shake: `sideEffects: false` is declared and locale modules are pure data exports.
- That means the practical size question is usually: what does this app actually import, not what is the smallest theoretical core in isolation?
How To Read It
- Use
mmntjswhen you want the broadest moment-compatible surface and can accept a heavier core. - Use
mmntjs/litewhen browser size matters and you are willing to add parsing, locale, or other extras explicitly. - Read locale size separately from core size. A single locale module is cheap; an all-locales browser build is where moment tends to bloat.
- Read timezone size separately from core size. Apps that do not need named IANA zones should not pay for timezone data at all.
Timezone Data
The IANA package is separate, and its compressed size is fairly modest.
- Packed timezone data moved from about 711 KB raw source blob to about 293 KB raw generated blob.
packages/timezone/dist/index.jsis about 316 KB raw and about 38.1 KB gzip after the pack-format migration.- That is why the timezone package is worth evaluating separately: it is not free, but it is smaller than many people assume for bundled IANA data.
Methodology
The interesting part is not only how the numbers were measured, but how the timezone package was made smaller in the first place.
Name dictionary encoding
Replace long zone names like America/New_York with short base-60 IDs, then materialize them at runtime.
Permutation-group index codec
Compress DST transition index patterns using run forms such as pair-repeat and increment. This is the most 'modern math' part of the timezone size work.
Delta frequency dictionary
Turn repeated timezone deltas into global dictionary IDs so frequent transition values collapse to short tokens.