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Babel timing

Build status Npm version

Measure Babel compilation time file by file, plugin by plugin.

Note: this project might be soon archived.


Profile Babel when your application or your tests take ages to build.

Note: this tool is in version 0, any minor release might introduce breaking changes.


npm i babel-timing -D
yarn add babel-timing -D


As standalone library via CLI

babel-timing path/to/file-1.js path/to/file-2.js
babel-timing path/to/file-*.js
babel-timing path/to/entrypoint.js --follow-imports

As standalone library via Node

const { babelTiming } = require('babel-timing');
const results = await babelTiming(['path/to/file.js'], options);

As Webpack integration

Profile Babel during the actual Webpack bundling process.

  1. Import babel-timing/webpack/plugin to Webpack configuration:
const BabelTimingPlugin = require('babel-timing/webpack/plugin');
  1. Add customize option to the existing babel-loader configuration:
module: {
  rules: [
      test: /\.m?js$/,
      use: {
        loader: 'babel-loader',
        options: {
          customize: require.resolve(
  1. Add babel-timing/webpack/plugin plugin (accepts the render options):
plugins: [new BabelTimingPlugin()];

...with options (accepts output and outputPath options):

plugins: [
  new BabelTimingPlugin({ output: 'json', outputPath: './results.json' }),
  1. Delete babel-loader cache at ./node_modules/.cache/babel-loader/

  2. Start Webpack bundling process and wait for results

As Jest integration

Profile Babel while running your actual Jest tests.

  1. Add the following transform and reporters entries to the existing Jest configuration:
  transform: {
    '^.+\\.jsx?$': 'babel-timing/jest/transformer'
  reporters: [

...with reporter's options (accepts the render options):

  reporters: [
      { output: 'json', outputPath: './results.json' },
  1. Run tests with --no-cache option

Further integrations


babelConfig / --babel-config

Type: string | false
Default: false

Path to a custom babel configuration file. By default Babel will try to load any existing valid configuration file.

followImports / --follow-imports

Type: bool
Default: false

Follow imported files/modules and run babel-timing against them.

include / --include

Type: string[] (cli accepts a string containing a comma-separated list)
Default: ['**']

Include paths (imported ones also) according to the provided glob patterns.

exclude / --exclude

Type: string[] (cli accepts a string containing a comma-separated list)
Default: ['**/node_modules/**']

Exclude paths (imported ones also) according to the provided glob patterns.

resolveMainFields / --resolve-main-fields

Type: string[] (cli accepts a string containing a comma-separated list)
Default: ['browser', 'module', 'main']

When importing from an npm package this option will determine which fields in its package.json are checked.

resolveExtensions / --resolve-extensions

Type: string[] (cli accepts a string containing a comma-separated list)
Default: ['.js', '.jsx', '.mjs', '.ts']

Attempt to resolve these extensions in order. Any other extension won't be considered.

--read-results (CLI only, for Node use render API)

Type: string
Default: undefined

Skip compilation and render existing results from file at specified path.

Render options

output / --output

Type: string
Default: "return" ("console" when called via CLI or integrations)
Options: "return", "console", "json"

Make babel-timing results available as:

  • "return" return results' object
  • "console" render results in console
  • "json" save results as babel-timing-results.json

outputPath / --output-path

Type: string
Default: "./babel-timing-results.json"

Path of output file in case output option is set to "json".

paginationSize / --pagination-size

Type: number
Default: 10

Number of entries displayed in a page when rendering "console" output.

aggregateBy / --aggregate-by

Type: string
Default: "files"
Options: "files", "plugins"

Output results aggregated by files or plugins.

expandPackages / --expand-packages

Type: bool
Default: false

Expand results relative to node_modules packages file by file.

How it works

Compile files with Babel 7 and get collect compilation info through wrapPluginVisitorMethod Babel config option.


Compilation info are by default extracted into the following data structure:

type ResultList = {
  name: string; // file name
  time: number; // total compilation time
  // compilation info by babel plugin
  plugins: {
    name: string;
    time: number;
    timePerVisit: number;
    visits: number;


This tool started as an attempt of measuring the time taken by Babel while running transpiled tests and compiling Webpack applications.

The main difficulty of monitoring Babel while running the aforementioned tools, consists of relating the wrapPluginVisitorMethod calls to the files actually being compiled.

Any further idea/contribution to get to a better Babel profiling solution is welcome.

Manual tests :)

node cli.js __fixtures__/file-1.js
node cli.js __fixtures__/file-1.js __fixtures__/file-2.js
node cli.js __fixtures__/*.js
node cli.js __fixtures__/entry.js --follow-imports


These API's are meant to integrate babel-timing with any bundler/tool using Babel.

new Timer(filename)

Timer class returns timer instances used to hook Babel's wrapPluginVisitorMethod, keep track of transform times and return a ResultList entry object for a given file.

const { Timer } = require('babel-timing');
const timer = new Timer(fileName);

// This is the function to be provided to Babel's "wrapPluginVisitorMethod" option

// Called after Babel transformations, returns "Results" object for given file


Utility function meant to temporarily store Timer instances into a Node module while Babel compiles.

const { timersCollection } = require('babel-timing');

// Returns Timer instance for given file. Creates a new `Timer` instance if no timer for given file is found

// Returns an array containing all the stored Timer instances


render(ResultList, options)

Accepts a ResultList array and renders an interactive CLI visualisation or outputs a JSON file of it.

const { render } = require('babel-timing');
render(babelTimingResults, { options });

Accepts the render options.

Thanks to


  • Add csv output option
  • Provide a wider set of integrations (rollup, babelify, parcel, ...)
  • Improve existing integrations
  • Consider versioning results JSON data shape
  • Consider splitting standalone feature from core and integrations