astring

library1.9.0jsnpmunverified

Astring is a lightweight and high-performance JavaScript code generator that transforms an ESTree-compliant Abstract Syntax Tree (AST) back into JavaScript source code. Currently at version 1.9.0, the library sees frequent minor and patch releases, indicating active development and responsiveness to new language features and bug fixes. Its key differentiators include exceptional speed (outperforming alternatives like Babel, Escodegen, and Prettier by significant margins), a tiny footprint (approx. 4 KB gzipped), and zero runtime dependencies. Astring supports JavaScript up to ES2024 and stage 3 proposals, can be extended with custom AST node handlers, and integrates with source map and comment generation tools. It's compatible with ASTs produced by parsers such as Acorn and Meriyah, and runs in Node.js, browsers, and Deno.

serialization

npm install astring

github ↗package ↗

INSTALL

IMPORT

SIG · ASTRING

astring

serializationjavascriptv1.9.0

Install

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Import

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Disk

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Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

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

generate

✓ import { generate } from 'astring';

✗ const generate = require('astring');

Astring primarily uses named exports. For CommonJS, use `const { generate } = require('astring');` for named destructuring.

GENERATOR

✓ import { GENERATOR } from 'astring';

✗ const { GENERATOR } = require('astring');

The base generator object, useful for extending Astring's code generation logic with custom handlers for specific AST node types. The CommonJS equivalent `require` also uses named destructuring.

astring (global)

✓ // In HTML: <script src="astring.min.js"></script> // In JS: var generate = astring.generate;

✗ import { generate } from './dist/astring.min.js';

The `dist/astring.min.js` bundle exposes `astring` as a global variable in browser environments, not as an ESM module for direct import.

This quickstart demonstrates parsing a JavaScript string into an ESTree AST using Acorn, then generating formatted code from that AST using Astring, including comments and custom indentation. It also shows using environment variables for dynamic values.

import { generate } from 'astring'; import * as acorn from 'acorn'; // npm install acorn const sourceCode = ` const add = (a, b) => { // This is a simple addition function return a + b; }; function subtract(x, y) { return x - y; } const result = add(process.env.NUM_ONE ?? '5', process.env.NUM_TWO ?? '3'); console.log('Result:', result); `; // Parse the source code into an ESTree-compliant AST const ast = acorn.parse(sourceCode, { ecmaVersion: 2024, // Use a recent ECMAScript version sourceType: 'module', }); // Generate code from the AST with specific options const generatedCode = generate(ast, { indent: ' ', // Use 2 spaces for indentation lineEnd: '\n', // Use newline for line endings comments: true, // Enable comment generation }); console.log('--- Original Source ---\n' + sourceCode); console.log('\n--- Generated Code ---\n' + generatedCode);

Debug

Known issues

gotchaAstring relies on `String.prototype.repeat` and `String.prototype.endsWith`. If targeting older JavaScript environments (e.g., IE) that lack these methods, you must include appropriate polyfills (e.g., `string.prototype.repeat`, `string.prototype.endsWith`, or `babel-polyfill`) for Astring to function correctly.

fix

For older environments, install and import polyfills like `npm install string.prototype.repeat string.prototype.endsWith` and `import 'string.prototype.repeat'; import 'string.prototype.endsWith';`

affects: >=1.0.0

gotchaAstring expects an ESTree-compliant AST. Feeding it a malformed or non-compliant AST, or one generated by a parser with significant deviations from the ESTree spec, may result in incorrect code generation or runtime errors.

fix

Ensure your AST is generated by a reputable, ESTree-compliant parser (e.g., Acorn, Meriyah, Espree) and matches the expected structure for Astring's handlers.

affects: >=1.0.0

gotchaEnabling comment generation (`comments: true`) or providing complex custom generators can impact performance. While Astring is designed for speed, these options add overhead and should be considered carefully in performance-critical applications.

fix

Only enable `comments: true` or use custom generators when necessary. For maximum performance in production, disable comment generation if comments are not required in the output.

affects: >=1.0.0

Errors

Common errors & fixes

TypeError: generate is not a function

Attempting to use `require('astring')` or `import generate from 'astring'` when `generate` is a named export.

fix

Use correct named import syntax: `import { generate } from 'astring';` for ESM or `const { generate } = require('astring');` for CommonJS.

TypeError: Cannot read properties of undefined (reading 'type')

The AST node being processed by `astring.generate` is either `undefined`, `null`, or does not conform to the expected ESTree structure (e.g., missing a `type` property).

fix

Inspect the input AST to ensure it's a valid ESTree-compliant object and that all its nodes have a `type` property. This often happens if the parsing failed or a transformation corrupted the AST.

Upgrade

Version history

1.9.0latest on npm

Audit

Dependencies

No dependency data recorded yet.

Agent activity

16 hits · last 30 days

node

OpenAI (training)

Resources

githubhttps://github.com/davidbonnet/astring ↗

packagehttps://www.npmjs.com/package/astring ↗