Bundle Size Guardian

Keeping the bundle small

The package is published as ESM + CJS with TypeScript declarations. The published size is enforced by size-limit via the test:size step that runs after every build. This skill explains the rules and how to fix overages.

The current budget

From .size-limit.json:

These are un-gzipped sizes (gzip: false, brotli: false). When you raise the limit, justify it in the PR description and update both numbers together if both grew.

Tree-shaking is on — keep it that way

package.json declares "sideEffects": false. Bundlers can therefore drop any module the user didn't import. To preserve this guarantee:

1. Never run effectful code at module top-level. No console.log, no global registration, no Object.defineProperty(globalThis, ...). Top-level should only declare constants/types/functions.
2. Don't import modules just for side effects. A bare import "./foo" is a side effect and will pin foo in the bundle.
3. Keep index.ts files re-export-only. Every existing src/modules/<name>/index.ts only contains export ... from "./...". Mirror that.
4. Prefer named exports over default exports. The repo uses named exports everywhere; tree-shakers handle them more reliably across CJS/ESM dual builds.

The .skip.ts / .skip.json convention

Files ending in .skip.ts or .skip.json hold heavy lookup data (lists of bank prefixes, city codes, plate codes, etc.). The naming is a project convention with two purposes:

1. Code review signal — the .skip suffix tells reviewers "this file is data, not logic; please scan but don't dwell."
2. Coverage exclusion — vitest.config.ts does not specifically exclude .skip.ts, but tests don't need to cover data files; reviewers expect that.

Examples already in the codebase:

src/modules/banksRegex/data.skip.json
src/modules/getBankNameFromCardNumber/banksCode.skip.ts
src/modules/getPlaceByIranNationalId/nationalId.skip.ts
src/modules/getPlaceByIranNationalId/provincesCodes.skip.ts
src/modules/numberplate/codes.skip.ts
src/modules/numberplate/types.skip.ts
src/modules/sheba/codes.skip.ts

When you add a new dataset:

• Put it in src/modules/<yourModule>/<descriptive>.skip.ts.
• Export it as const NAME = {...} as const; — the as const keeps the inferred type narrow without bloating runtime size.
• Import it only from the module that uses it. Do not re-export it from src/index.ts (that would force every consumer to ship it).
• If the dataset is JSON-shaped, prefer .skip.json + import data from "./data.skip.json" assert { type: "json" } (see src/modules/banksRegex/index.ts:1).

Bundler configuration — don't touch unless you mean to

bunup.config.ts enables:

The big banner/footer comments (bunup.config.ts:31-118) are emitted before minification and survive into the published bundle. They cost ~3 kB. Don't expand them.

When bun run test:size fails

The postbuild step runs bun run test:size, which is size-limit. A failure looks like:

Package size limit has exceeded by 12.3 KB
  Size limit:   860 KB
  Size:         872.3 KB

Diagnose, then fix

1. Find what grew. Compare with master:

   git stash && bun run build && du -b build/index.mjs
   git stash pop && bun run build && du -b build/index.mjs
   

   The delta tells you how much your change added.
2. Check the build report — bunup prints brotli/gzip sizes per chunk during the build. Identify the chunk that grew.
3. Locate the offending symbol. Most common causes:
   • A new dataset checked in as a regular .ts file (not .skip.ts) and re-exported from src/index.ts.
   • A function that pulled in a heavy dependency at module top-level instead of inside the function body.
   • A Map or Set literal that should have been declared as const and shipped as a plain object.
   • Duplicated regex tables — check if one of the existing constants in src/modules/digits/digits.constants.ts already has what you need.
4. Fix without expanding the budget. Move heavy data to .skip.ts, lazy-load with a dynamic import() for genuinely optional features, or eliminate duplication.
5. If the budget legitimately must rise, edit .size-limit.json and call it out in the PR description. The previous bumps in git log -- .size-limit.json are good examples of what justification looks like.

Types budget (100 kB)

Types can grow surprisingly fast when:

• A module exports a deep union/intersection that TypeScript serializes literally.
• A large as const literal is re-exported with its full type rather than a narrowed signature.
• unknown/any is replaced with a giant inferred type.

Mitigations:

• Type the public return as the narrow interface (BankInfo), not the literal as const value.
• Use export type { Foo } from "./types" rather than export * from a types file when you only need a subset.
• Avoid infer in public types — push it into the implementation file and export the resolved type.

Dependencies — be conservative

The only runtime dependency is fastest-levenshtein (see package.json). Before adding any new dependencies entry, ask:

1. Is the helper small enough to vendor (≤ ~50 lines)?
2. Does it have its own dependencies? They count toward consumers' install size.
3. Does it support ESM + CJS dual export? If not, it will break our build.

devDependencies are free — go wild.

Checklist before opening a PR that touches code size

• bun run build succeeds and bun run test:size passes locally.
• New data files use the .skip.ts (or .skip.json) suffix.
• No bare import "./foo" (side-effect imports).
• No top-level statements with side effects in new files.
• If size limit was bumped, the PR description says why and quotes the new number.

References

• .size-limit.json — the source of truth for budgets
• bunup.config.ts — bundler config
• package.json — "sideEffects": false
• Existing data files: src/modules/sheba/codes.skip.ts, src/modules/getBankNameFromCardNumber/banksCode.skip.ts
• size-limit docs: https://github.com/ai/size-limit