levn

library0.4.1jsnpmunverified

Levn is a JavaScript library for parsing human-readable string input into structured JavaScript values, leveraging type validation. It is designed for concise, human-authored data, such as configuration files or command-line arguments, distinguishing itself from JSON by prioritizing human readability, conciseness, and built-in type validation via `type-check`. It supports regex and date literals and is extensible with custom types. Unlike JSON, it is not optimized for large-scale data transport due to its parsing overhead. The current stable version is 0.4.1. This package appears to be largely unmaintained, with its last npm publish over six years ago and minimal activity on its GitHub repository in recent years.

serialization

npm install levn

github ↗package ↗

INSTALL

IMPORT

SIG · LEVN

levn

serializationjavascriptv0.4.1

Install

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Import

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Disk

—

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.

parse

✓ const { parse } = require('levn');

✗ import { parse } from 'levn';

Levn is a CommonJS module, primarily designed for Node.js environments with `require`. Direct ESM `import` is not supported.

parsedTypeParse

✓ const { parsedTypeParse } = require('levn');

✗ import parsedTypeParse from 'levn/parsedTypeParse';

`parsedTypeParse` requires a pre-parsed type object, typically obtained from the `type-check` library. It's a named export from the main `levn` module.

VERSION

✓ const { VERSION } = require('levn');

✗ const VERSION = require('levn').VERSION;

The `VERSION` string is a direct named export, not a property off the default export.

Demonstrates basic `parse` usage for various types (Number, String, Boolean, Array, Object) and the `parsedTypeParse` function with a pre-parsed type from `type-check`.

const { parse } = require('levn'); const { parseType } = require('type-check'); // Assuming 'type-check' is installed // Basic type parsing console.log('Number 2:', parse('Number', '2')); console.log('String "levn":', parse('String', 'levn')); console.log('Boolean true:', parse('Boolean', 'true')); // Complex types and implicit delimiters console.log('Array of Numbers:', parse('[Number]', '1,2,3')); console.log('Object with properties:', parse('{a: String, b: Number}', 'a: str, b: 2')); // Parsing with pre-parsed types (from type-check) const parsedNumberArrayType = parseType('[Number]'); console.log('Parsed Type Array:', parse('parsedTypeParse', parsedNumberArrayType, '4,5,6'));

Debug

Known issues

breakingLevn is an abandoned package. Its last major update was in 2013-2014, and the last npm publish was six years ago. It relies on very old Node.js versions (>=0.8.0). Use in modern environments without careful consideration and potential polyfills is not recommended and may lead to compatibility issues or security vulnerabilities through its dependencies.

fix

Consider modern alternatives like `yaml`, `toml`, or robust JSON parsers. If `levn` is critical, fork the project, update dependencies, and address any Node.js compatibility issues.

affects: All versions

gotchaLevn is a CommonJS-only module. Attempting to use `import` statements (ESM syntax) will result in runtime errors in Node.js environments unless transpiled or configured correctly with a CommonJS wrapper.

fix

Always use `require()` for importing `levn` and its functions: `const { parse } = require('levn');`.

affects: All versions

gotchaThe library explicitly states it is slower and less efficient than JSON for transporting large amounts of data. Its purpose is for human-entered, concise data, not machine-to-machine communication.

fix

Do not use `levn` for performance-critical data serialization/deserialization involving large payloads. Stick to its intended use case for small, human-editable configuration or command-line inputs.

affects: All versions

gotchaLevn's parsing heavily relies on the `type-check` library for its type format and validation. Developers need to understand `type-check`'s syntax and capabilities to effectively use `levn` for complex data structures.

fix

Familiarize yourself with the `type-check` library's documentation, especially its type format, before attempting advanced parsing with `levn`.

affects: All versions

Errors

Common errors & fixes

TypeError: require is not a function

Attempting to use `require` in an ECMAScript Module (ESM) context without proper configuration.

fix

Ensure your project is configured for CommonJS, or use dynamic `import()` if absolutely necessary within an ESM file. `levn` is designed for CommonJS (`require`).

Error: Cannot find module 'type-check'

`type-check`, a core dependency, is missing from `node_modules`.

fix

Install the peer dependency: `npm install type-check`.

SyntaxError: Unexpected token '...' (or similar parsing errors)

Input string does not conform to Levn's syntax rules or the specified type, or contains unrecognized literals.

fix

Review the Levn format documentation and ensure the input string correctly matches the `type` string provided to the `parse` function. Pay attention to delimiters and value formats (e.g., dates with `#`, regex with `/`).

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

The `levn` module was not successfully imported, or `require('levn')` returned `undefined` or an unexpected value.

fix

Verify that `levn` is installed (`npm list levn`) and that the `require` path is correct. Ensure no other module is inadvertently shadowing `levn`.

Upgrade

Version history

0.4.1latest on npm

Audit

Dependencies

type-checkrequiredUsed for its type format and to validate parsed values.

prelude-lsrequiredA utility library, likely for functional programming constructs, though not directly exposed in the main API.

Agent activity

7 hits · last 30 days

node

Amazon

Resources

githubhttps://github.com/gkz/levn ↗

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