Calculate the real cost to run
Size Limit is a performance budget tool for JavaScript. It checks every commit on CI, calculates the real cost of your JS for end-users and throws an error if the cost exceeds the limit.
ES modules and tree-shaking support. Add Size Limit to Travis CI, Circle CI, GitHub Actions or another CI system to know if a pull request adds a massive dependency. Modular to fit different use cases: big JS applications that use their own bundler or small npm libraries with many files. Can calculate the time it would take a browser to download and execute your JS. Time is a much more accurate and understandable metric compared to the size in bytes. Calculations include all dependencies and polyfills used in your JS.
With GitHub action Size Limit will post bundle size changes as a comment in pull request discussion.
With --why, Size Limit can tell you why your library is of this size
and show the real cost of all your internal dependencies.
We are using Statoscope for this analysis.
file, webpack, time)
and 3 plugin presets for popular use cases (app, big-lib, small-lib).
A CLI tool finds plugins in package.json and loads the config.
If you use the webpack plugin, Size Limit will bundle your JS files into
a single file. It is important to track dependencies and webpack polyfills.
It is also useful for small libraries with many small files and without
a bundler.
The webpack plugin creates an empty webpack project, adds your library
and looks for the bundle size difference.
The time plugin compares the current machine performance with that of
a low-priced Android devices to calculate the CPU throttling rate.
Then the time plugin runs headless Chrome (or desktop Chrome if it’s
available) to track the time a browser takes to compile and execute your JS.
Note that these measurements depend on available resources and might
be unstable. See here
for more details.
Usage
JS Applications
Suitable for applications that have their own bundler and send the JS bundle directly to a client (without publishing it to npm). Think of a user-facing app or website, like an email client, a CRM, a landing page or a blog with interactive elements, using React/Vue/Svelte lib or vanilla JS.
Show instructions
Install the preset:
npm install --save-dev size-limit @size-limit/file
Add the size-limit section and the size script to your package.json:
+ "size-limit": [ + { + "path": "dist/app-*.js" + } + ], "scripts": { "build": "webpack ./webpack.config.js", + "size": "npm run build && size-limit", "test": "jest && eslint ." }
Here’s how you can get the size for your current project:
$ npm run size Package size: 30.08 kB with all dependencies, minified and gzipped
Now, let’s set the limit. Add 25% to the current total size and use that as
the limit in your package.json:
"size-limit": [ { + "limit": "35 kB", "path": "dist/app-*.js" } ],
Add the size script to your test suite:
"scripts": { "build": "webpack ./webpack.config.js", "size": "npm run build && size-limit", - "test": "jest && eslint ." + "test": "jest && eslint . && npm run size" }
If you don’t have a continuous integration service running, don’t forget to add one — start with Travis CI.
File size limit (in kB) is not the best way to describe your JS application cost for developers. Developers will compare the size of the JS bundle with the size of images. But browsers need much more time to parse 100 kB of JS than 100 kB of an image since JS compilers are very complex.
This is why Size Limit support time-based limit. It runs headless Chrome to track the time a browser takes to compile and execute your JS.
Show instructions
Install the preset:
npm install --save-dev size-limit @size-limit/preset-app
Add the size-limit section and the size script to your package.json:
+ "size-limit": [ + { + "path": "dist/app-*.js" + } + ], "scripts": { "build": "webpack ./webpack.config.js", + "size": "npm run build && size-limit", "test": "jest && eslint ." }
Here’s how you can get the size for your current project:
$ npm run size Package size: 30.08 kB with all dependencies, minified and gzipped Loading time: 602 ms on slow 3G Running time: 214 ms on Snapdragon 410 Total time: 815 ms
Now, let’s set the limit. Add 25% to the current total time and use that as
the limit in your package.json:
"size-limit": [ { + "limit": "1 s", "path": "dist/app-*.js" } ],
Add the size script to your test suite:
"scripts": { "build": "webpack ./webpack.config.js", "size": "npm run build && size-limit", - "test": "jest && eslint ." + "test": "jest && eslint . && npm run size" }
If you don’t have a continuous integration service running, don’t forget to add one — start with Travis CI.
JS libraries > 10 kB in size.
This preset includes headless Chrome, and will measure your lib’s execution time. You likely don’t need this overhead for a small 2 kB lib, but for larger ones the execution time is a more accurate and understandable metric that the size in bytes. Libraries like React are good examples for this preset.
Show instructions
Install preset:
npm install --save-dev size-limit @size-limit/preset-big-lib
Add the size-limit section and the size script to your package.json:
+ "size-limit": [ + { + "path": "dist/react.production-*.js" + } + ], "scripts": { "build": "webpack ./scripts/rollup/build.js", + "size": "npm run build && size-limit", "test": "jest && eslint ." }
If you use ES modules you can test the size after tree-shaking with import
option:
"size-limit": [ { "path": "dist/react.production-*.js", + "import": "{ createComponent }" } ],
Here’s how you can get the size for your current project:
$ npm run size Package size: 30.08 kB with all dependencies, minified and gzipped Loading time: 602 ms on slow 3G Running time: 214 ms on Snapdragon 410 Total time: 815 ms
Now, let’s set the limit. Add 25% to the current total time and use that
as the limit in your package.json:
"size-limit": [ { + "limit": "1 s", "path": "dist/react.production-*.js" } ],
Add a size script to your test suite:
"scripts": { "build": "rollup ./scripts/rollup/build.js", "size": "npm run build && size-limit", - "test": "jest && eslint ." + "test": "jest && eslint . && npm run size" }
If you don’t have a continuous integration service running, don’t forget to add one — start with Travis CI.
Add the library size to docs, it will help users to choose your project:
# Project Name Short project description * **Fast.** 10% faster than competitor. + * **Small.** 15 kB (minified and gzipped). + [Size Limit](https://github.com/ai/size-limit) controls the size.
JS libraries < 10 kB in size.
This preset will only measure the size, without the execution time, so it’s suitable for small libraries. If your library is larger, you likely want the Big Libraries preset above. Nano ID or Storeon are good examples for this preset.
Show instructions
First, install size-limit:
npm install --save-dev size-limit @size-limit/preset-small-lib
Add the size-limit section and the size script to your package.json:
+ "size-limit": [ + { + "path": "index.js" + } + ], "scripts": { + "size": "size-limit", "test": "jest && eslint ." }
Here’s how you can get the size for your current project:
$ npm run size Package size: 177 B with all dependencies, minified and gzipped
If your project size starts to look bloated, run --why for analysis:
npm run size -- --why
We use Statoscope as bundle analyzer.
Now, let’s set the limit. Determine the current size of your library,
add just a little bit (a kilobyte, maybe) and use that as the limit
in your package.json:
"size-limit": [ { + "limit": "9 kB", "path": "index.js" } ],
Add the size script to your test suite:
"scripts": { "size": "size-limit", - "test": "jest && eslint ." + "test": "jest && eslint . && npm run size" }
If you don’t have a continuous integration service running, don’t forget to add one — start with Travis CI.
Add the library size to docs, it will help users to choose your project:
# Project Name Short project description * **Fast.** 10% faster than competitor. + * **Small.** 500 bytes (minified and gzipped). No dependencies. + [Size Limit](https://github.com/ai/size-limit) controls the size.
Size Limit has a GitHub action that comments and rejects pull requests based on Size Limit output.
Install and configure Size Limit as shown above. Add the following action inside.github/workflows/size-limit.yml
name: "size" on: pull_request: branches: - master jobs: size: runs-on: ubuntu-latest env: CI_JOB_NUMBER: 1 steps: - uses: actions/checkout@v1 - uses: andresz1/size-limit-action@v1 with: github_token: ${{ secrets.GITHUB_TOKEN }} Config Plugins and Presets
Plugins or plugin presets will be loaded automatically from package.json.
For example, if you want to use @size-limit/webpack, you can just use
npm install --save-dev @size-limit/webpack, or you can use our preset
@size-limit/preset-big-lib.
Plugins:
@size-limit/file checks the size of files with Gzip, Brotli
or without compression.
@size-limit/webpack adds your library to empty webpack project
and prepares bundle file for file plugin.
@size-limit/webpack-why adds reports for webpack plugin
about your library is of this size to show the cost of all your
dependencies.
@size-limit/webpack-css adds css support for webpack plugin.
@size-limit/esbuild is like webpack plugin, but uses esbuild
to be faster and use less space in node_modules.
@size-limit/esbuild-why add reports for esbuild plugin
about your library is of this size to show the cost of all your
dependencies.
@size-limit/time uses headless Chrome to track time to execute JS.
@size-limit/dual-publish compiles files to ES modules with dual-publish
to check size after tree-shaking.
Plugin presets:
@size-limit/preset-app contains file and time plugins.
@size-limit/preset-big-lib contains webpack, file, and time plugins.
@size-limit/preset-small-lib contains esbuild and file plugins.
Third-Party Plugins
Third-party plugins and presets named starting with size-limit- are also supported.
For example:
size-limit-node-esbuild
is like @size-limit/esbuild but for Node libraries.
size-limit-preset-node-lib
is like @size-limit/preset-small-lib but for Node libraries which contains
above node-esbuild and core file plugins.
nx-size-limit
is an NX build system community plugin.
Limits Config
Size Limits supports three ways to define limits config.
size-limit section in package.json:
"size-limit": [ { "path": "index.js", "import": "{ createStore }", "limit": "500 ms" } ]
or a separate .size-limit.json config file:
[ { "path": "index.js", "import": "{ createStore }", "limit": "500 ms" } ]
or a more flexible .size-limit.js or .size-limit.cjs config file:
module.exports = [ { path: "index.js", import: "{ createStore }", limit: "500 ms" } ]
Each section in the config can have these options:
path: relative paths to files. The only mandatory option. It could be a path"index.js", a pattern "dist/app-*.js"
or an array ["index.js", "dist/app-*.js", "!dist/app-exclude.js"].
import: partial import to test tree-shaking. It could be "{ lib }"
to test import { lib } from 'lib', * to test all exports,
or { "a.js": "{ a }", "b.js": "{ b }" } to test multiple files.
limit: size or time limit for files from the path option. It should be
a string with a number and unit, separated by a space.
Format: 100 B, 10 kB, 500 ms, 1 s.
name: the name of the current section. It will only be useful
if you have multiple sections.
entry: when using a custom webpack config, a webpack entry could be given.
It could be a string or an array of strings.
By default, the total size of all entry points will be checked.
webpack: with false it will disable webpack.
running: with false it will disable calculating running time.
gzip: with false it will disable gzip compression.
brotli: with true it will use brotli compression and disable
gzip compression.
config: a path to a custom webpack config.
ignore: an array of files and dependencies to exclude from
the project size calculation.
modifyWebpackConfig: (.size-limit.js only) function that can be used
to do last-minute changes to the webpack config, like adding a plugin.
compareWith: path to stats.json from another build to compare
(when --why is using).
uiReports: custom UI reports list (see Statoscope docs).
If you use Size Limit to track the size of CSS files, make sure to set
webpack: false. Otherwise, you will get wrong numbers, because webpack
inserts style-loader runtime (≈2 kB) into the bundle.
--why
You can run size-limit --why to analyze the bundle.
You will need to install @size-limit/esbuild-why or @size-limit/webpack-why
depends on which bundler you are using (default is esbuild).
For @size-limit/esbuild-why,
it will generate a esbuild-why.html at the current directory & open it in the browser.
If you also specify --save-bundle <DIR>,
the report will be generated inside <DIR>.
If you have multiple sections in your config,
the files will be named esbuild-why-{n}.html,
or you can give it a custom name:
[ { "name": "cjs", /* snap */ }, { "name": "esm", /* snap */ } ]
This will produce esbuild-why-cjs.html and esbuild-why-esm.html respectively.
For @size-limit/webpack-why,
it will generate the report and open it in the browser automatically.
const sizeLimit = require('size-limit') const filePlugin = require('@size-limit/file') const webpackPlugin = require('@size-limit/webpack') sizeLimit([filePlugin, webpackPlugin], [filePath]).then(result => { result //=> { size: 12480 } })
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