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what is esrap fr?

sveltejs/esrap — explained in plain English

Analysis updated 2026-07-04 · repo last pushed 2026-06-27

136JavaScriptAudience · developerComplexity · 2/5ActiveSetup · easy

tl;dr

esrap takes a structured code tree (AST) and prints it back out as readable, runnable code with sourcemaps. It's a lightweight alternative to heavy formatters for generating code from structures you already have.

vibe map

mindmap
  root((esrap))
    What it does
      AST to code
      Generates sourcemaps
      Lightweight output
    Tech stack
      JavaScript
      TypeScript
      TSX
    Use cases
      Code editors
      Compilers
      Refactoring tools
    Audience
      Developer tool builders
      Compiler authors
    Philosophy
      Minimalist
      Not Prettier

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what do people make with this?

VIBE 1

Build a code refactoring tool that modifies a tree and prints clean TypeScript output.

VIBE 2

Create a code editor feature that reorganizes or simplifies a user's JavaScript automatically.

VIBE 3

Develop a custom compiler that transforms and emits readable code with sourcemaps for debugging.

VIBE 4

Define custom language rules to generate code from a structured format for niche or experimental languages.

what's the stack?

JavaScriptTypeScriptTSX

how it stacks up fr

sveltejs/esrapbuynao/aipathcobusgreyling/loop-engineering
Stars136131141
LanguageJavaScriptJavaScriptJavaScript
Last pushed2026-06-27
MaintenanceActive
Setup difficultyeasyeasyeasy
Complexity2/52/53/5
Audiencedevelopergeneraldeveloper

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

how do i run it?

Difficulty · easy time til it works · 30min

Requires understanding AST structures and defining or using existing language rules to generate output.

No license information was provided in the explanation, so default copyright restrictions may apply.

in plain english

esrap is a tool that turns code structure back into readable code. Most tools parse code from text into a structured format (an Abstract Syntax Tree, or AST), but esrap does the opposite: it takes that structured tree and prints it out as actual code you can read and run. It also generates sourcemaps, which means if you ever need to debug the output, your tools can trace it back to the original source. At a high level, you hand esrap a JavaScript object that represents your code's logic, things like function calls, variables, and expressions, along with a set of rules for the language you are targeting. The tool then walks through that structure, piece by piece, and writes out the corresponding text. If your input structure includes location data from the original file, esrap automatically creates a sourcemap so tools like browsers and editors can connect the generated output back to where it came from. Anyone building developer tools, like code editors, compilers, or automated code refactoring apps, would find this useful. For example, if you build a tool that reorganizes or simplifies a user's JavaScript, you would parse their original code into a tree, modify that tree programmatically, and then use esrap to print the updated tree back into clean, readable TypeScript. It ships with built-in support for TypeScript and TSX, but you can also define your own custom languages and rules for printing any kind of structure you want. What stands out about the project is its minimalist philosophy. The README directly addresses why you might choose this over Prettier (a very popular code formatter): "Because it's ginormous." esrap is designed to be a lightweight, focused alternative for generating code from a structure you already have, rather than a heavy tool that parses and formats everything from scratch.

prompts (copy fr)

prompt 1
I have a JavaScript AST object representing a function. How do I use esrap to print it back out as readable TypeScript code?
prompt 2
Show me how to configure esrap with custom printing rules for my own domain-specific language structure.
prompt 3
I modified an AST in my refactoring tool. How do I use esrap to generate the output code and a sourcemap that maps back to the original file?
prompt 4
How do I use esrap to print TSX code from a structured tree instead of using Prettier for formatting?

Frequently asked questions

what is esrap fr?

esrap takes a structured code tree (AST) and prints it back out as readable, runnable code with sourcemaps. It's a lightweight alternative to heavy formatters for generating code from structures you already have.

What language is esrap written in?

Mainly JavaScript. The stack also includes JavaScript, TypeScript, TSX.

Is esrap actively maintained?

Active — commit in last 30 days (last push 2026-06-27).

What license does esrap use?

No license information was provided in the explanation, so default copyright restrictions may apply.

How hard is esrap to set up?

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

Who is esrap for?

Mainly developer.

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