Registry / devops / import-cost-core

import-cost-core

library5.5.0jsnpmunverified

Calculate the bundle size of imported packages in JavaScript and TypeScript with a CLI and Node.js API. Version 5.5.0, actively maintained (2025 release). Powered by esbuild and es-module-lexer for high performance — scans 50+ files in less than a second. Provides minified, gzipped, and brotli sizes; identifies tree-shakeable packages; supports budget enforcement, JSON output, ignore patterns, watch mode, and git diff for CI/CD. Works with npm, pnpm, yarn, and bun. Aims to be a drop-in replacement for the deprecated import-cost VS Code extension backend, offering more accuracy and speed than webpack-bundle-analyzer or cost-of-modules.

devops

npm install import-cost-core

github ↗package ↗

INSTALL

IMPORT

SIG · IMPORT-COST-CORE

import-cost-core

devopsjavascriptv5.5.0

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

importCost

✓ import { importCost } from 'import-cost-core'

Main function; returns an EventEmitter. Available since v1.

Lang

✓ import { Lang } from 'import-cost-core'

Enum for file language: Lang.JAVASCRIPT, Lang.TYPESCRIPT, Lang.VUE, Lang.SVELTE.

PackageInfo

✓ import type { PackageInfo } from 'import-cost-core'

✗ import { PackageInfo } from 'import-cost-core'

PackageInfo is a TypeScript type/interface, not a runtime value. Must use 'import type'.

cleanup

✓ import { cleanup } from 'import-cost-core'

Must be called on shutdown to terminate esbuild workers.

Demonstrates API usage: scanning a TypeScript file for imports and logging size metrics with cleanup.

import { importCost, cleanup, Lang } from 'import-cost-core'; import type { PackageInfo } from 'import-cost-core'; const fileName = 'src/index.ts'; const fileContents = ` import express from 'express'; import { readFile } from 'fs/promises'; const _ = require('lodash'); `; const emitter = importCost(fileName, fileContents, Lang.TYPESCRIPT); emitter.on('start', (packages: PackageInfo[]) => { console.log('Calculating sizes for', packages.length, 'packages...'); }); emitter.on('calculated', (pkg: PackageInfo) => { console.log(`${pkg.name}: minified=${(pkg.size / 1024).toFixed(2)} KB, gzip=${(pkg.gzip / 1024).toFixed(2)} KB, brotli=${(pkg.brotli / 1024).toFixed(2)} KB, tree-shakeable=${pkg.sideEffects === false}`); }); emitter.on('done', (packages: PackageInfo[]) => { console.log('All done!'); cleanup(); }); emitter.on('error', (err: Error) => { console.error('Error:', err.message); });

import-cost --version

Debug

Known issues

gotchaThe `importCost` function caches results based on file content. If you call it multiple times with the same content, you might get stale results. Dispose the emitter and create a new one for fresh calculations.

fix

Call `emitter.removeAllListeners()` before creating a new emitter for the same file.

affects: >=1.0

gotchaThe `PackageInfo` import is a TypeScript type, not a value. Attempting to use it at runtime will throw `ReferenceError: Cannot access 'PackageInfo' before initialization` in CommonJS or `PackageInfo is not defined` in ESM.

fix

Use `import type { PackageInfo } from 'import-cost-core'` to import only the type, or use `import { PackageInfo } from 'import-cost-core'` only if you need the runtime value (it does not exist).

affects: >=1.0

deprecatedThe default export `import importCost from 'import-cost-core'` is deprecated as of v3.0. Use named imports instead.

fix

Replace `import importCost from 'import-cost-core'` with `import { importCost } from 'import-cost-core'`.

affects: >=3.0

breakingIn v2.0, the function signature changed: `importCost(fileName, fileContents, language)` replaced the old `importCost(fileName, fileContents, language, config)`. The config object is now passed as the fourth argument, but the third argument is now required (previously optional).

fix

Update to v3.0+ which restored the optional config parameter or adjust your calls to include the language parameter.

affects: >=2.0 <3.0

gotchaThe `cleanup` function must be called to terminate background esbuild workers. If you don't call it, the Node.js process will not exit cleanly (it will hang).

fix

Call `cleanup()` when done, e.g., after the 'done' event or in a process 'exit' handler.

affects: >=1.0

Errors

Common errors & fixes

ReferenceError: Cannot access 'PackageInfo' before initialization

Importing `PackageInfo` as a value when it is only a TypeScript type.

fix

Use `import type { PackageInfo } from 'import-cost-core'` instead.

Error: Cannot find module 'import-cost-core'

Package not installed or not in node_modules.

fix

Run `npm install import-cost-core` in your project.

TypeError: importCost is not a function

Using default import in ESM when package expects named export, or misconfiguring bundler.

fix

Use `import { importCost } from 'import-cost-core'`.

Error: esbuild is not installed

Missing peer dependency 'esbuild'.

fix

Run `npm install esbuild` alongside import-cost-core.

Upgrade

Version history

5.5.0latest on npm

Audit

Dependencies

esbuildrequiredCore bundler used for size calculation

es-module-lexerrequiredFast ESM module analysis for tree-shaking detection

Agent activity

4 hits · last 30 days

node

Resources

githubhttps://github.com/ruban-s/import-cost ↗

packagehttps://www.npmjs.com/package/import-cost-core ↗