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wtf is prepack?

gaearon/prepack — explained in plain English

Analysis updated 2026-07-17 · repo last pushed 2018-08-31

★ 7JavaScriptAudience · developerComplexity · 4/5DormantSetup · moderate

TL;DR

Prepack pre-computes parts of your JavaScript ahead of time so it has less setup work to do at runtime.

Mindmap

mindmap
  root((prepack))
    What it does
      Precomputes JS
      Rewrites code
      Bakes in results
    Tech stack
      JavaScript
      Webpack
      Rollup
    Use cases
      Speed up startup
      Reduce init logic
      Build pipeline tool
    Audience
      Web developers
      App teams

Code map

Detail Auto

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filefunction / class

Why would anyone build with this?

REASON 1

Reduce startup time for a JavaScript bundle with heavy initialization logic.

REASON 2

Plug Prepack into a Webpack or Rollup build pipeline to pre-optimize code.

REASON 3

Try Prepack's interactive playground to see how it transforms sample code.

What's in the stack?

JavaScriptWebpackRollup

How it stacks up

gaearon/prepackboneskull/promwrapbrunosimon/ecole-multimedia-fi-dev2-2019
Stars777
LanguageJavaScriptJavaScriptJavaScript
Last pushed2018-08-312020-07-212021-08-12
MaintenanceDormantDormantDormant
Setup difficultymoderateeasyhard
Complexity4/52/52/5
Audiencedeveloperdeveloperdeveloper

Figures from each repo's GitHub metadata at analysis time.

How do you spin it up?

Difficulty · moderate Time to first run · 30min

Integrates with existing bundlers, but conformance with all JS features is still a work in progress.

Yoink these prompts

Prompt 1
Show me how to add Prepack to my Webpack build pipeline to speed up startup.
Prompt 2
Help me identify which parts of my JavaScript initialization code Prepack could precompute.
Prompt 3
Explain what kinds of JavaScript features Prepack might not fully support yet.

Frequently asked questions

wtf is prepack?

Prepack pre-computes parts of your JavaScript ahead of time so it has less setup work to do at runtime.

What language is prepack written in?

Mainly JavaScript. The stack also includes JavaScript, Webpack, Rollup.

Is prepack actively maintained?

Dormant — no commits in 2+ years (last push 2018-08-31).

How hard is prepack to set up?

Setup difficulty is rated moderate, with roughly 30min to a first successful run.

Who is prepack for?

Mainly developer.

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