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JSLint, The JavaScript Code Quality and Coverage Tool

Douglas Crockford douglas@crockford.com

Status

Branch master
(v2026.6.30)
beta
(Web Demo)
alpha
(Development)
CI ci ci ci
Coverage coverage coverage coverage
Demo
Artifacts



Web Demo

screenshot



Web Demo Archived



Table of Contents

  1. Quickstart Install

  2. Quickstart JSLint Report

  3. Quickstart V8 Coverage Report

  4. Quickstart JSLint in CodeMirror

  5. Quickstart JSLint in Vim

  6. Quickstart JSLint in VSCode

  7. Documentation

  8. Package Listing

  9. Changelog

  10. License

  11. Devops Instruction



Quickstart Install



To install, just download and save https://www.jslint.com/jslint.mjs to file:

#!/bin/sh

curl -L https://www.jslint.com/jslint.mjs > jslint.mjs
  • shell output

screenshot



To run jslint.mjs in shell:

#!/bin/sh

printf "console.log('hello world');\n" > hello.js

node jslint.mjs hello.js
  • shell output

screenshot



To import jslint.mjs in ES Module environment:

#!/bin/sh

node --input-type=module --eval '

/*jslint devel*/

// Import JSLint in ES Module environment.

import jslint from "./jslint.mjs";

let globals = ["caches", "indexedDb"];
let options = {browser: true};
let result;
let source = "console.log(\u0027hello world\u0027);\n";

// JSLint <source> and print <formatted_message>.

result = jslint.jslint(source, options, globals);
result.warnings.forEach(function ({
    formatted_message
}) {
    console.error(formatted_message);
});

'
  • shell output

screenshot



To import jslint.mjs in CommonJS environment:

#!/bin/sh

node --eval '

/*jslint devel*/
(async function () {
    let globals = ["caches", "indexedDb"];
    let jslint;
    let options = {browser: true};
    let result;
    let source = "console.log(\u0027hello world\u0027);\n";

// Import JSLint in CommonJS environment.

    jslint = await import("./jslint.mjs");
    jslint = jslint.default;

// JSLint <source> and print <formatted_message>.

    result = jslint.jslint(source, options, globals);
    result.warnings.forEach(function ({
        formatted_message
    }) {
        console.error(formatted_message);
    });
}());

'
  • shell output

screenshot



To JSLint entire directory in shell:

#!/bin/sh

# JSLint directory '.'

node jslint.mjs .
  • shell output

screenshot



Quickstart JSLint Report



To create a JSLint report in shell:

#!/bin/sh

printf "function foo() {console.log('hello world');}\n" > hello.js

# Create JSLint report from file 'hello.js' in shell.

node jslint.mjs \
    jslint_report=.artifact/jslint_report_hello.html \
    hello.js
  • shell output

screenshot

screenshot



To create a JSLint report in javascript:

#!/bin/sh

node --input-type=module --eval '

/*jslint devel*/
import jslint from "./jslint.mjs";
import fs from "fs";
(async function () {
    let result;
    let source = "function foo() {console.log(\u0027hello world\u0027);}\n";

// Create JSLint report from <source> in javascript.

    result = jslint.jslint(source);
    result = jslint.jslint_report(result);
    result = `<body class="JSLINT_ JSLINT_REPORT_">\n${result}</body>\n`;

    await fs.promises.mkdir(".artifact/", {recursive: true});
    await fs.promises.writeFile(".artifact/jslint_report_hello.html", result);
    console.error("wrote file .artifact/jslint_report_hello.html");
}());

'
  • shell output

screenshot

screenshot



Quickstart V8 Coverage Report



To create V8 coverage report from Node.js / Npm program in shell:

#!/bin/sh

git clone https://github.com/tryghost/node-sqlite3 node-sqlite3-sh \
    --branch=v5.0.11 \
    --depth=1 \
    --single-branch

cd node-sqlite3-sh
npm install

# Create V8 coverage report from program `npm run test` in shell.

node ../jslint.mjs \
    v8_coverage_report=../.artifact/coverage_sqlite3_sh/ \
        --exclude=tes?/ \
        --exclude=tes[!0-9A-Z_a-z-]/ \
        --exclude=tes[0-9A-Z_a-z-]/ \
        --exclude=tes[^0-9A-Z_a-z-]/ \
        --exclude=test/**/*.js \
        --exclude=test/suppor*/*elper.js \
        --exclude=test/suppor?/?elper.js \
        --exclude=test/support/helper.js \
        --include=**/*.cjs \
        --include=**/*.js \
        --include=**/*.mjs \
        --include=li*/*.js \
        --include=li?/*.js \
        --include=lib/ \
        --include=lib/**/*.js \
        --include=lib/*.js \
        --include=lib/sqlite3.js \
    npm run test
  • shell output

screenshot

screenshot

screenshot



To create V8 coverage report from Node.js / Npm program in javascript:

#!/bin/sh

git clone https://github.com/tryghost/node-sqlite3 node-sqlite3-js \
    --branch=v5.0.11 \
    --depth=1 \
    --single-branch

cd node-sqlite3-js
npm install

node --input-type=module --eval '

/*jslint node*/
import jslint from "../jslint.mjs";
(async function () {

// Create V8 coverage report from program `npm run test` in javascript.

    await jslint.v8CoverageReportCreate({
        coverageDir: "../.artifact/coverage_sqlite3_js/",
        processArgv: [
            "--exclude=tes?/",
            "--exclude=tes[!0-9A-Z_a-z-]/",
            "--exclude=tes[0-9A-Z_a-z-]/",
            "--exclude=tes[^0-9A-Z_a-z-]/",
            "--exclude=test/**/*.js",
            "--exclude=test/suppor*/*elper.js",
            "--exclude=test/suppor?/?elper.js",
            "--exclude=test/support/helper.js",
            "--include=**/*.cjs",
            "--include=**/*.js",
            "--include=**/*.mjs",
            "--include=li*/*.js",
            "--include=li?/*.js",
            "--include=lib/",
            "--include=lib/**/*.js",
            "--include=lib/*.js",
            "--include=lib/sqlite3.js",
            "npm", "run", "test"
        ]
    });
}());

'
  • shell output

screenshot

screenshot

screenshot



Quickstart JSLint in CodeMirror

  1. Download and save jslint.mjs, jslint_wrapper_codemirror.js to file.

  2. Edit, save, and serve example html-file below:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>CodeMirror: JSLint Demo</title>

<!-- Assets from codemirror. -->

    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.10/codemirror.css">
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.10/addon/lint/lint.css">
    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.10/codemirror.js"></script>
    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.10/mode/javascript/javascript.js"></script>
    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.10/addon/lint/lint.js"></script>

<!-- Assets from jslint. -->

    <script type="module" src="./jslint.mjs?window_jslint=1"></script>
    <script defer src="./jslint_wrapper_codemirror.js"></script>
<style>
body {
    background: #bbb;
    color: #333;
    font-family: sans-serif;
    margin: 20px;
}
.JSLINT_.JSLINT_REPORT_ {
    margin-top: 20px;
}
#editor1 {
    height: 300px;
    width: 100%;
}
</style>
</head>


<body>
    <h1>CodeMirror: JSLint Demo</h1>
    <h3>
This demo will auto-lint the code below, and auto-generate a report as you type.
    </h3>

<!-- Container for codemirror-editor. -->

    <textarea id="editor1">console.log('hello world');</textarea>

<!-- Container for jslint-report. -->

    <div class="JSLINT_ JSLINT_REPORT_"></div>


<script type=module>
window.addEventListener("load", function () {
    let editor = window.CodeMirror.fromTextArea(document.getElementById(
        "editor1"
    ), {
        gutters: [
            "CodeMirror-lint-markers"
        ],
        indentUnit: 4,
        lineNumbers: true,
        lint: {
            lintOnChange: true, // Enable auto-lint.
            options: {
                // browser: true,
                // node: true
                globals: [
                    // "caches",
                    // "indexedDb"
                ]
            }
        },
        mode: "javascript"
    });

// Initialize event-handling before linter is run.

    editor.on("lintJslintBefore", function (/* options */) {
        // options.browser = true;
        // options.node = true;
        // options.globals = [
        //     "caches",
        //     "indexedDb"
        // ];
        return;
    });

// Initialize event-handling after linter is run.

    editor.on("lintJslintAfter", function (options) {

// Generate jslint-report from options.result.

        document.querySelector(
            ".JSLINT_REPORT_"
        ).innerHTML = window.jslint.jslint_report(options.result);
    });

// Manually trigger linter.

    editor.performLint();
});
</script>
</body>
</html>
  1. Live example at https://www.jslint.com/jslint_wrapper_codemirror.html

screenshot



Quickstart JSLint in Vim

  1. Download and save jslint.mjs, jslint_wrapper_vim.vim to directory ~/.vim/
  2. Add vim-command :source ~/.vim/jslint_wrapper_vim.vim to file ~/.vimrc
    • If above files were saved to custom-directory, then use that directory instead, e.g.:
  3. Vim can now jslint files (via nodejs):
    • with vim-command :SaveAndJslint
    • with vim-key-combo <Ctrl-S> <Ctrl-J>
  • screenshot

screenshot



Quickstart JSLint in VSCode

  1. In VSCode, search and install extension vscode-jslint
  2. In VSCode, while editing a javascript file:
    • right-click context-menu and select [JSLint - Lint File]
    • or use key-binding [Ctrl + Shift + J], [L]
    • or use key-binding [ Cmd + Shift + J], [L] for Mac
  • screenshot

screenshot



Documentation

  • jslint.mjs contains the jslint function. It parses and analyzes a source file, returning an object with information about the file. It can also take an object that sets options.
  • index.html runs the jslint.mjs function in a web page.



API Doc

screenshot



Directive


/*jslint beta*/
/*jslint beta*/
// Enable experimental warnings.
// Warn if global variables are redefined.
// Warn if const / let statements are not declared at top of function or
//    script, similar to var statements.
// Warn if const / let / var statements are not declared in ascii-order.
// Warn if named-functions are not declared in ascii-order.
// Warn if cases in switch-statements are not in ascii-order.

/*jslint bitwise*/
/*jslint bitwise*/
// Allow bitwise operator.

let foo = 0 | 1;

/*jslint browser*/
/*jslint browser*/
// Assume browser environment.

localStorage.getItem("foo");

/*jslint convert*/
/*jslint convert*/
// Allow conversion operator.

let foo = new Date() + "";
let bar = !!0;

/*jslint couch*/
/*jslint couch*/
// Assume CouchDb environment.

registerType("text-json", "text/json");

/*jslint devel*/
/*jslint devel*/
// Allow console.log() and friends.

console.log("hello");

/*jslint eval*/
/*jslint eval*/
// Allow eval().

eval("1");

/*jslint fart*/
/*jslint fart*/
// Allow complex fat-arrow.

let foo = async ({bar, baz}) => {
    return await bar(baz);
};

/*jslint for*/
/*jslint for*/
// Allow for-loop.

function foo() {
    let ii;
    for (ii = 0; ii < 10; ii += 1) {
        foo();
    }
}

/*jslint getset*/
/*jslint getset, this, devel*/
// Allow get() and set().

let foo = {
    bar: 0,
    get getBar() {
        return this.bar;
    },
    set setBar(value) {
        this.bar = value;
    }
};
console.log(foo.getBar); // 0
foo.setBar = 1;
console.log(foo.getBar); // 1

/*jslint indent2*/
/*jslint indent2*/
// Use 2-space indent.

function foo() {
  return;
}

/*jslint long*/
/*jslint long*/
// Allow long lines.

let foo = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";

/*jslint node*/
/*jslint node*/
// Assume Node.js environment.

require("fs");

/*jslint nomen*/
/*jslint nomen*/
// Allow weird property name.

let foo = {};
foo._bar = 1;

/*jslint single*/
/*jslint single*/
// Allow single-quote strings.

let foo = '';

/*jslint subscript*/
/*jslint subscript*/
// Allow identifiers in subscript-notation.

let foo = {};
foo["bar"] = 1;

/*jslint this*/
/*jslint this*/
// Allow 'this'.

function foo() {
    return this;
}

/*jslint trace*/
/*jslint trace*/
// Include jslint stack-trace in warnings.

console.log('hello world');
/*
1. Undeclared 'console'.
console.log('hello world');
Error
    at warn_at (...)
    at warn (...)
    at lookup (...)
    at pre_v (...)
    at jslint.mjs
2. Use double quotes, not single quotes.
console.log(...);
Error
    at warn_at (...)
    at lex_string (...)
    at lex_token (...)
    at jslint_phase2_lex (...)
    at Function.jslint (...)
    at jslint.mjs
*/

/*jslint unordered*/
/*jslint unordered*/
// Allow unordered cases, params, properties, variables, and exports.

let foo = {bb: 1, aa: 0};

function bar({
    bb = 1,
    aa = 0
}) {
    return aa + bb;
}

export {
    foo,
    bar
};

/*jslint white*/
/*jslint white*/
// Allow messy whitespace.

let foo = 1; let bar = 2;

/*global*/
/*global foo, bar*/
// Declare global variables foo, bar.

foo();
bar();

/*property*/
/*property foo, bar*/
// Restrict property-access to only .foo, .bar.

let aa = {bar: 1, foo: 2};

/*jslint-disable*/.../*jslint-enable*/
/*jslint-disable*/

JSLint will ignore and treat this region as blank-lines.
Syntax error.

/*jslint-enable*/

//jslint-ignore-line
// JSLint will ignore non-fatal warnings at given line.

eval("1"); //jslint-ignore-line

/*coverage-disable*/.../*coverage-enable*/
/*coverage-disable*/

// JSLint will ignore code-coverage in this region.

if (false) {
    console.log("hello world");
}

/*coverage-enable*/

//coverage-ignore-line
// JSLint will ignore code-coverage at given line.

if (false) {
    console.log("hello world"); //coverage-ignore-line
}



ECMAScript Feature Support

#. JSLint Support ES Version ES Feature
99. ES2027 Explicit Resource Management
98. ES2027 Atomics.pause
97. ES2027 Joint Iteration
96. ES2027 Temporal
95. ES2026 Upsert
94. ES2026 JSON.parse source text access
93. ES2026 Iterator Sequencing
92. ES2026 Uint8Array to/from Base64
91. ES2026 Math.sumPrecise
90. ES2026 Error.isError
89. ES2026 Array.fromAsync
88. ES2025 RegExp.escape
87. ES2025 Redeclarable global eval-introduced vars
86. ES2025 Float16 on TypedArrays, DataView, Math.f16round
85. ES2025 Promise.try
84. ES2025 Sync Iterator helpers
83. ES2025 JSON Modules
82. ES2025 Import Attributes
81. ES2025 RegExp Modifiers
80. ES2025 New Set methods
79. ES2025 Duplicate named capture groups
78. ES2024 ArrayBuffer transfer
77. ES2024 Promise.withResolvers
76. ES2024 Array Grouping
75. ES2024 Resizable and growable ArrayBuffers
74. ⚠️ ES2024 RegExp v flag with set notation + properties of strings
73. ES2024 Atomics.waitAsync
72. ES2024 Well-Formed Unicode Strings
71. ES2023 Change Array by Copy
70. ES2023 Symbols as WeakMap keys
69. ES2023 Hashbang Grammar
68. ES2023 Array find from last
67. ES2022 Error Cause
66. ES2022 Class Static Block
65. ES2022 Accessible Object.prototype.hasOwnProperty
64. ES2022 .at()
63. ES2022 Ergonomic brand checks for Private Fields
62. ES2022 Top-level await
61. ES2022 RegExp Match Indices
60. ES2022 Class Public Instance Fields & Private Instance Fields
59. ES2021 Numeric separators
58. ES2021 Logical Assignment Operators
57. ES2021 WeakRefs
56. ES2021 Promise.any
55. ES2021 String.prototype.replaceAll
54. ES2020 import.meta
53. ES2020 Nullish coalescing Operator
52. ES2020 Optional Chaining
51. ES2020 for-in mechanics
50. ES2020 globalThis
49. ES2020 Promise.allSettled
48. ES2020 BigInt
47. ES2020 import()
46. ES2020 String.prototype.matchAll
45. ES2019 Array.prototype.{flat,flatMap}
44. ES2019 String.prototype.{trimStart,trimEnd}
43. ES2019 Well-formed JSON.stringify
42. ES2019 Object.fromEntries
41. ES2019 Function.prototype.toString revision
40. ES2019 Symbol.prototype.description
39. ES2019 JSON superset
38. ES2019 Optional catch binding
37. ES2018 Asynchronous Iteration
36. ES2018 Promise.prototype.finally
35. ES2018 RegExp Unicode Property Escapes
34. ES2018 RegExp Lookbehind Assertions
33. ES2018 Rest/Spread Properties
32. ES2018 RegExp named capture groups
31. ES2018 s (dotAll) flag for regular expressions
30. ES2018 Lifting template literal restriction
29. ES2017 Shared memory and atomics
28. ES2017 Async functions
27. ⚠️ ES2017 Trailing commas in function parameter lists and calls
26. ES2017 Object.getOwnPropertyDescriptors
25. ES2017 String padding
24. ES2017 Object.values/Object.entries
23. ES2016 Exponentiation operator
22. ES2016 Array.prototype.includes
21. ES2015 arrows
20. ES2015 classes
19. ES2015 enhanced object literals
18. ES2015 template strings
17. ES2015 destructuring
16. ES2015 default + rest + spread
15. ES2015 let + const
14. ES2015 iterators + for..of
13. ES2015 generators
12. ES2015 unicode
11. ⚠️ ES2015 modules
10. ES2015 module loaders
9. ES2015 map + set + weakmap + weakset
8. ES2015 proxies
7. ES2015 symbols
6. ES2015 subclassable built-ins
5. ES2015 promises
4. ES2015 math + number + string + array + object APIs
3. ES2015 binary and octal literals
2. ES2015 reflect api
1. ES2015 tail calls



Package Listing

screenshot_package_listing.svg



Changelog

screenshot_changelog.svg



License



Devops Instruction



pull-request merge

  1. update .github/workflows/ci.yml .github/workflows/publish.yml to:

  2. update CHANGELOG.md

    • verify <CHANGELOG.md entry #1> is most-relevant to pull-request.
    • run
      # re-run until version propagates
      npm run test2
      
      # update 'PR-xxx' placeholder
      sh jslint_ci.sh shGithubPrUpdatePrxxx
      
      # re-run until version propagates
      sh jslint_ci.sh shGithubPrCreate alpha beta # v20yy.mm.dd __pr_beta_pre
      
      git push upstream alpha -f
  3. goto https://github.com/jslint-org/jslint/compare/beta...kaizhu256:jslint:branch-p2026.7.3

    • click Create pull request
    • input Add a title * with: <CHANGELOG.md entry #1>
    • input Add a description with:
      Fixes #xxx.
      
      This PR will:
      <CHANGELOG.md entry #1>
      
      This PR will additionally:
      <CHANGELOG.md entry extra>
      
      <screenshot>
      
    • click Preview and review
    • verify:
      • base respository: jslint-org/jslint
      • base: beta
    • click Create pull request
  4. wait awhile before continuing ...



branch-master commit

  1. update .github/workflows/ci.yml .github/workflows/publish.yml to:

  2. update CHANGELOG.md

    • verify <CHANGELOG.md entry #1> is most-relevant to pull-request.
    • run
      # re-run until version propagates
      npm run test2
      
      # update 'PR-xxx' placeholder
      sh jslint_ci.sh shGithubPrUpdatePrxxx
      
      # re-run until version propagates
      sh jslint_ci.sh shGithubPrCreate alpha master # v20yy.mm.dd __pr_master_pre
      
      git push upstream alpha -f
  3. goto https://github.com/jslint-org/jslint/compare/beta...kaizhu256:jslint:branch-v2026.6.30

  4. wait awhile before continuing ...



branch-master publish

  1. goto https://www.npmjs.com/package/@jslint-org/jslint/access
    • click Github Actions
    • input Organization or user* with: jslint-org
    • input Repository* with: jslint
    • input Workflow filename* with: publish.yml
    • click Set up connection or Update Package Settings
  2. goto https://github.com/jslint-org/jslint/releases/new
    • input Tag: Select tag with: v20yy.mm.dd
      • click Create new tag and click Create
      • verify correct-year v20yy.mm.dd
      • select Target: master
    • input Release title with: v20yy.mm.dd - <CHANGELOG.md entry #1>
      • select Previous tag: Auto
      • click Generate release notes
    • input Write with:
      <CHANGELOG.md entry #1>
      <CHANGELOG.md entry extra>
      
      **Full Changelog**: ...
      
    • click Preview and review
    • click Latest
    • click Publish release



vscode-jslint publish

  1. goto https://github.com/jslint-org/jslint/tree/gh-pages/branch-beta/.artifact/jslint_wrapper_vscode
    • click vscode-jslint-20yy.mm.dd.vsix
    • click Raw to download
  2. goto https://marketplace.visualstudio.com/manage/publishers/jslint
    • move mouse to version-number, right-click, and select Update
    • upload downloaded file vscode-jslint-20yy.mm.dd.vsix
    • click 'Upload'
      • verify email-notification [Succeeded] Extension publish on Visual Studio Marketplace - vscode-jslint