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eslint

Wed, 24 Sep 2025 15:28:00 +0800

eslint/eslint

ESLint

ESLint is a tool for identifying and reporting on patterns found in ECMAScript/JavaScript code. In many ways, it is similar to JSLint and JSHint with a few exceptions:

ESLint uses Espree for JavaScript parsing.
ESLint uses an AST to evaluate patterns in code.
ESLint is completely pluggable, every single rule is a plugin and you can add more at runtime.

Installation and Usage

Prerequisites: Node.js (^18.18.0, ^20.9.0, or >=21.1.0) built with SSL support. (If you are using an official Node.js distribution, SSL is always built in.)

You can install and configure ESLint using this command:

`1`	`npm init @eslint/config@latest`

After that, you can run ESLint on any file or directory like this:

`1`	`npx eslint yourfile.js`

pnpm Installation

To use ESLint with pnpm, we recommend setting up a .npmrc file with at least the following settings:

1
2

auto-install-peers=true
node-linker=hoisted

This ensures that pnpm installs dependencies in a way that is more compatible with npm and is less likely to produce errors.

Configuration

You can configure rules in your eslint.config.js files as in this example:

import { defineConfig } from "eslint/config";

export default defineConfig([
	{
		files: ["**/*.js", "**/*.cjs", "**/*.mjs"],
		rules: {
			"prefer-const": "warn",
			"no-constant-binary-expression": "error",
		},
	},
]);

The names "prefer-const" and "no-constant-binary-expression" are the names of rules in ESLint. The first value is the error level of the rule and can be one of these values:

"off" or 0 - turn the rule off
"warn" or 1 - turn the rule on as a warning (doesn’t affect exit code)
"error" or 2 - turn the rule on as an error (exit code will be 1)

The three error levels allow you fine-grained control over how ESLint applies rules (for more configuration options and details, see the configuration docs).

Version Support

The ESLint team provides ongoing support for the current version and six months of limited support for the previous version. Limited support includes critical bug fixes, security issues, and compatibility issues only.

ESLint offers commercial support for both current and previous versions through our partners, Tidelift and HeroDevs.

See Version Support for more details.

Code of Conduct

ESLint adheres to the OpenJS Foundation Code of Conduct.

Filing Issues

Before filing an issue, please be sure to read the guidelines for what you’re reporting:

Frequently Asked Questions

Does ESLint support JSX?

Yes, ESLint natively supports parsing JSX syntax (this must be enabled in configuration). Please note that supporting JSX syntax is not the same as supporting React. React applies specific semantics to JSX syntax that ESLint doesn’t recognize. We recommend using eslint-plugin-react if you are using React and want React semantics.

Does Prettier replace ESLint?

No, ESLint and Prettier have different jobs: ESLint is a linter (looking for problematic patterns) and Prettier is a code formatter. Using both tools is common, refer to Prettier’s documentation to learn how to configure them to work well with each other.

What ECMAScript versions does ESLint support?

ESLint has full support for ECMAScript 3, 5, and every year from 2015 up until the most recent stage 4 specification (the default). You can set your desired ECMAScript syntax and other settings (like global variables) through configuration.

What about experimental features?

ESLint’s parser only officially supports the latest final ECMAScript standard. We will make changes to core rules in order to avoid crashes on stage 3 ECMAScript syntax proposals (as long as they are implemented using the correct experimental ESTree syntax). We may make changes to core rules to better work with language extensions (such as JSX, Flow, and TypeScript) on a case-by-case basis.

In other cases (including if rules need to warn on more or fewer cases due to new syntax, rather than just not crashing), we recommend you use other parsers and/or rule plugins. If you are using Babel, you can use @babel/eslint-parser and @babel/eslint-plugin to use any option available in Babel.

Once a language feature has been adopted into the ECMAScript standard (stage 4 according to the TC39 process), we will accept issues and pull requests related to the new feature, subject to our contributing guidelines. Until then, please use the appropriate parser and plugin(s) for your experimental feature.

Which Node.js versions does ESLint support?

ESLint updates the supported Node.js versions with each major release of ESLint. At that time, ESLint’s supported Node.js versions are updated to be:

The most recent maintenance release of Node.js
The lowest minor version of the Node.js LTS release that includes the features the ESLint team wants to use.
The Node.js Current release

ESLint is also expected to work with Node.js versions released after the Node.js Current release.

Refer to the Quick Start Guide for the officially supported Node.js versions for a given ESLint release.

Where to ask for help?

Open a discussion or stop by our Discord server.

Why doesn’t ESLint lock dependency versions?

Lock files like package-lock.json are helpful for deployed applications. They ensure that dependencies are consistent between environments and across deployments.

Packages like eslint that get published to the npm registry do not include lock files. npm install eslint as a user will respect version constraints in ESLint’s package.json. ESLint and its dependencies will be included in the user’s lock file if one exists, but ESLint’s own lock file would not be used.

We intentionally don’t lock dependency versions so that we have the latest compatible dependency versions in development and CI that our users get when installing ESLint in a project.

The Twilio blog has a deeper dive to learn more.

Releases

We have scheduled releases every two weeks on Friday or Saturday. You can follow a release issue for updates about the scheduling of any particular release.

Security Policy

ESLint takes security seriously. We work hard to ensure that ESLint is safe for everyone and that security issues are addressed quickly and responsibly. Read the full security policy.

Semantic Versioning Policy

ESLint follows semantic versioning. However, due to the nature of ESLint as a code quality tool, it’s not always clear when a minor or major version bump occurs. To help clarify this for everyone, we’ve defined the following semantic versioning policy for ESLint:

Patch release (intended to not break your lint build)
- A bug fix in a rule that results in ESLint reporting fewer linting errors.
- A bug fix to the CLI or core (including formatters).
- Improvements to documentation.
- Non-user-facing changes such as refactoring code, adding, deleting, or modifying tests, and increasing test coverage.
- Re-releasing after a failed release (i.e., publishing a release that doesn’t work for anyone).
Minor release (might break your lint build)
- A bug fix in a rule that results in ESLint reporting more linting errors.
- A new rule is created.
- A new option to an existing rule that does not result in ESLint reporting more linting errors by default.
- A new addition to an existing rule to support a newly-added language feature (within the last 12 months) that will result in ESLint reporting more linting errors by default.
- An existing rule is deprecated.
- A new CLI capability is created.
- New capabilities to the public API are added (new classes, new methods, new arguments to existing methods, etc.).
- A new formatter is created.
- eslint:recommended is updated and will result in strictly fewer linting errors (e.g., rule removals).
Major release (likely to break your lint build)
- eslint:recommended is updated and may result in new linting errors (e.g., rule additions, most rule option updates).
- A new option to an existing rule that results in ESLint reporting more linting errors by default.
- An existing formatter is removed.
- Part of the public API is removed or changed in an incompatible way. The public API includes:
  - Rule schemas
  - Configuration schema
  - Command-line options
  - Node.js API
  - Rule, formatter, parser, plugin APIs

According to our policy, any minor update may report more linting errors than the previous release (ex: from a bug fix). As such, we recommend using the tilde (~) in package.json e.g. "eslint": "~3.1.0" to guarantee the results of your builds.

License

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Team

These folks keep the project moving and are resources for help.

Technical Steering Committee (TSC)

The people who manage releases, review feature requests, and meet regularly to ensure ESLint is properly maintained.

Nicholas C. Zakas

Francesco Trotta

Milos Djermanovic

Reviewers

The people who review and implement new features.

唯然	Nitin Kumar

Committers

The people who review and fix bugs and help triage issues.

fnx

Josh Goldberg ✨

Tanuj Kanti

루밀LuMir

Website Team

Team members who focus specifically on eslint.org

Amaresh S M

Harish

Percy Ma

simdjson

Tue, 16 Sep 2025 15:28:32 +0800

simdjson/simdjson

simdjson : Parsing gigabytes of JSON per second

JSON is everywhere on the Internet. Servers spend a *lot* of time parsing it. We need a fresh approach. The simdjson library uses commonly available SIMD instructions and microparallel algorithms to parse JSON 4x faster than RapidJSON and 25x faster than JSON for Modern C++.

Fast: Over 4x faster than commonly used production-grade JSON parsers.
Record Breaking Features: Minify JSON at 6 GB/s, validate UTF-8 at 13 GB/s, NDJSON at 3.5 GB/s.
Easy: First-class, easy to use and carefully documented APIs.
Strict: Full JSON and UTF-8 validation, lossless parsing. Performance with no compromises.
Automatic: Selects a CPU-tailored parser at runtime. No configuration needed.
Reliable: From memory allocation to error handling, simdjson’s design avoids surprises.
Peer Reviewed: Our research appears in venues like VLDB Journal, Software: Practice and Experience.

This library is part of the Awesome Modern C++ list.

Real-world usage

If you are planning to use simdjson in a product, please work from one of our releases.

Quick Start

The simdjson library is easily consumable with a single .h and .cpp file.

Prerequisites: g++ (version 7 or better) or clang++ (version 6 or better), and a 64-bit system with a command-line shell (e.g., Linux, macOS, freeBSD). We also support programming environments like Visual Studio and Xcode, but different steps are needed. Users of clang++ may need to specify the C++ version (e.g., c++ -std=c++17) since clang++ tends to default on C++98.

Pull simdjson.h and simdjson.cpp into a directory, along with the sample file twitter.json. You can download them with the wget utility:

wget https://raw.githubusercontent.com/simdjson/simdjson/master/singleheader/simdjson.h https://raw.githubusercontent.com/simdjson/simdjson/master/singleheader/simdjson.cpp https://raw.githubusercontent.com/simdjson/simdjson/master/jsonexamples/twitter.json

Create quickstart.cpp:

#include <iostream>
#include "simdjson.h"
using namespace simdjson;
int main(void) {
    ondemand::parser parser;
    padded_string json = padded_string::load("twitter.json");
    ondemand::document tweets = parser.iterate(json);
    std::cout << uint64_t(tweets["search_metadata"]["count"]) << " results." << std::endl;
}

c++ -o quickstart quickstart.cpp simdjson.cpp
./quickstart

`1`	`100 results.`

Documentation

Usage documentation is available:

Basics is an overview of how to use simdjson and its APIs.
Builder is an overview of how to efficiently write JSON strings using simdjson.
Performance shows some more advanced scenarios and how to tune for them.
Implementation Selection describes runtime CPU detection and how you can work with it.
API contains the automatically generated API documentation.

Godbolt

Some users may want to browse code along with the compiled assembly. You want to check out the following lists of examples:

Performance results

The simdjson library uses three-quarters less instructions than state-of-the-art parser RapidJSON. To our knowledge, simdjson is the first fully-validating JSON parser to run at gigabytes per second (GB/s) on commodity processors. It can parse millions of JSON documents per second on a single core.

The following figure represents parsing speed in GB/s for parsing various files on an Intel Skylake processor (3.4 GHz) using the GNU GCC 10 compiler (with the -O3 flag). We compare against the best and fastest C++ libraries on benchmarks that load and process the data. The simdjson library offers full unicode (UTF-8) validation and exact number parsing.

The simdjson library offers high speed whether it processes tiny files (e.g., 300 bytes) or larger files (e.g., 3MB). The following plot presents parsing speed for synthetic files over various sizes generated with a script on a 3.4 GHz Skylake processor (GNU GCC 9, -O3).

All our experiments are reproducible.

For NDJSON files, we can exceed 3 GB/s with our multithreaded parsing functions.

Packages

Bindings and Ports of simdjson

We distinguish between “bindings” (which just wrap the C++ code) and a port to another programming language (which reimplements everything).

ZippyJSON: Swift bindings for the simdjson project.
libpy_simdjson: high-speed Python bindings for simdjson using libpy.
pysimdjson: Python bindings for the simdjson project.
cysimdjson: high-speed Python bindings for the simdjson project.
simdjson-rs: Rust port.
simdjson-rust: Rust wrapper (bindings).
SimdJsonSharp: C# version for .NET Core (bindings and full port).
simdjson_nodejs: Node.js bindings for the simdjson project.
simdjson_php: PHP bindings for the simdjson project.
simdjson_ruby: Ruby bindings for the simdjson project.
fast_jsonparser: Ruby bindings for the simdjson project.
simdjson-go: Go port using Golang assembly.
rcppsimdjson: R bindings.
simdjson_erlang: erlang bindings.
simdjsone: erlang bindings.
lua-simdjson: lua bindings.
hermes-json: haskell bindings.
zimdjson: Zig port.
simdjzon: Zig port.
JSON-Simd: Raku bindings.
JSON::SIMD: Perl bindings; fully-featured JSON module that uses simdjson for decoding.
gemmaJSON: Nim JSON parser based on simdjson bindings.
simdjson-java: Java port.

About simdjson

The simdjson library takes advantage of modern microarchitectures, parallelizing with SIMD vector instructions, reducing branch misprediction, and reducing data dependency to take advantage of each CPU’s multiple execution cores.

Our default front-end is called On-Demand, and we wrote a paper about it:

John Keiser, Daniel Lemire, On-Demand JSON: A Better Way to Parse Documents?, Software: Practice and Experience 54 (6), 2024.

Some people enjoy reading the first (2019) simdjson paper: A description of the design and implementation of simdjson is in our research article:

Geoff Langdale, Daniel Lemire, Parsing Gigabytes of JSON per Second, VLDB Journal 28 (6), 2019.

We have an in-depth paper focused on the UTF-8 validation:

John Keiser, Daniel Lemire, Validating UTF-8 In Less Than One Instruction Per Byte, Software: Practice & Experience 51 (5), 2021.

We also have an informal blog post providing some background and context.

For the video inclined,

(It was the best voted talk, we’re kinda proud of it.)

Funding

The work is supported by the Natural Sciences and Engineering Research Council of Canada under grants RGPIN-2017-03910 and RGPIN-2024-03787.

Contributing to simdjson

Head over to CONTRIBUTING.md for information on contributing to simdjson, and HACKING.md for information on source, building, and architecture/design.

License

This code is made available under the Apache License 2.0 as well as under the MIT License. As a user, you can pick the license you prefer.

Under Windows, we build some tools using the windows/dirent_portable.h file (which is outside our library code): it is under the liberal (business-friendly) MIT license.

For compilers that do not support C++17, we bundle the string-view library which is published under the Boost license. Like the Apache license, the Boost license is a permissive license allowing commercial redistribution.

For efficient number serialization, we bundle Florian Loitsch’s implementation of the Grisu2 algorithm for binary to decimal floating-point numbers. The implementation was slightly modified by JSON for Modern C++ library. Both Florian Loitsch’s implementation and JSON for Modern C++ are provided under the MIT license.

For runtime dispatching, we use some code from the PyTorch project licensed under 3-clause BSD.

Parsing on Producthunt daily

eslint

eslint/eslint

ESLint

Table of Contents

Installation and Usage

pnpm Installation

Configuration

Version Support

Code of Conduct

Filing Issues

Frequently Asked Questions

Does ESLint support JSX?

Does Prettier replace ESLint?

What ECMAScript versions does ESLint support?

What about experimental features?

Which Node.js versions does ESLint support?

Where to ask for help?

Why doesn’t ESLint lock dependency versions?

Releases

Security Policy

Semantic Versioning Policy

License

Team

Technical Steering Committee (TSC)

Reviewers

Committers

Website Team

Sponsors

Platinum Sponsors

Gold Sponsors

Silver Sponsors

Bronze Sponsors

Technology Sponsors

simdjson

simdjson/simdjson

simdjson : Parsing gigabytes of JSON per second

Table of Contents

Real-world usage

Quick Start

Documentation

Godbolt

Performance results

Packages

Bindings and Ports of simdjson

About simdjson

Funding

Contributing to simdjson

License