JSLint, The JavaScript Code Quality and Coverage Tool

Douglas Crockford douglas@crockford.com

Status

Web Demo

• https://www.jslint.com

Web Demo Archived

• Web Demo 2020
• Web Demo 2014 (ES5 only)
• Web Demo 2013 (ES5, CSS, HTML)

Table of Contents

1. Quickstart Install

   • To install, just download and save https://www.jslint.com/jslint.mjs to file:
   • To run jslint.mjs in shell:
   • To import jslint.mjs in ES Module environment:
   • To import jslint.mjs in CommonJS environment:
   • To JSLint entire directory in shell:

2. Quickstart Autofix Whitespace

   • To autofix whitespace in shell:
   • To autofix whitespace in javascript:

3. Quickstart JSLint Report

   • To create a JSLint report in shell:
   • To create a JSLint report in javascript:

4. Quickstart V8 Coverage Report

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

5. Quickstart JSLint in CodeMirror

6. Quickstart JSLint in Vim

7. Quickstart JSLint in VSCode

8. Documentation

   • API Doc
   • Directive
     • /*jslint*/
     • /*global*/
     • /*property*/
     • /*jslint-disable*/ ... /*jslint-enable*/
     • //jslint-ignore-line
     • /*coverage-disable*/ ... /*coverage-enable*/
     • //coverage-ignore-line
   • ECMAScript Feature Support

9. Package Listing

10. Changelog

11. License

12. Devops Instruction

    • pull-request merge
    • branch-master commit
    • branch-master publish
    • vscode-jslint qa
    • vscode-jslint publish

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

To run jslint.mjs in shell:

#!/bin/sh

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

node jslint.mjs hello.js

• shell output

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

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

To JSLint entire directory in shell:

#!/bin/sh

# JSLint directory '.'

node jslint.mjs .

• shell output

Quickstart Autofix Whitespace

To autofix whitespace in shell:

#!/bin/sh

printf '
/*jslint devel*/
console.log(
"hello world");
' > hello_autofix.js

node jslint.mjs jslint_autofix=hello_autofix.js

cat hello_autofix.js

• shell output

To autofix whitespace in javascript:

#!/bin/sh

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

/*jslint devel*/
import jslint from "./jslint.mjs";
let result;
let source = (`
/*jslint devel*/
console.log(
"hello world");
`);

result = jslint.jslint(source, {autofix: true});
console.log(result.autofixed);

'

• shell output

Quickstart JSLint Report

To create a JSLint report in shell:

#!/bin/sh

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

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

node jslint.mjs \
    jslint_report=.artifact/jslint_report_hello.html \
    hello_report.js

• shell output

• screenshot file .artifact/jslint_report_hello.html

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 file .artifact/jslint_report_hello.html

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=v6.0.1 \
    --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 file .artifact/coverage_sqlite3_sh/index.html

• screenshot file .artifact/coverage_sqlite3_sh/lib/sqlite3.js.html

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=v6.0.1 \
    --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 file .artifact/coverage_sqlite3_js/index.html

• screenshot file .artifact/coverage_sqlite3_js/lib/sqlite3.js.html

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/5.65.21/codemirror.css" integrity="sha512-7vaQ4LLdaXd2IuMd4MUQ6LRFIGbEwJI1aq6KYqL3RjbdQyUkRFhwZKmqmkBXurTFdGlx687lTN8FSJfX6Df8Gw==" crossorigin="anonymous">
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.21/addon/lint/lint.css" integrity="sha512-rx8Dv9UY+C/6Qsech6A5L2ka9ugVuQfdGlNitUbYtbuEMjfo5JapbOyUOwRAwvl7GmZfYiP5t4qOE5+d8aKgbA==" crossorigin="anonymous">
    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.21/codemirror.js" integrity="sha512-ksE4KDA1cKB0p1MTQsoUZ5lpj+KvHOreU76sE+4RsG92LiyIE7gUrnT3Dt+O7CrC2aJzG17UsOh7apakp7lyJw==" crossorigin="anonymous"></script>
    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.21/mode/javascript/javascript.js" integrity="sha512-VgqsGo4zxSK9KBf4c3RWpFWkRfBEeIUb2p5VqKtDj7sXdTyTyx38jVVJSriVU12pS5hG5J69FDi/LDsQ5Y1Ldw==" crossorigin="anonymous"></script>
    <script defer src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.21/addon/lint/lint.js" integrity="sha512-HzWWmsisNY6OUHWrNyo4yiHkGs6CUGEwI8Pu+q9tCWkmeWtvWa7D1gHTx9Oj0LQdldSKd4yffFA4PObCeKi9ew==" crossorigin="anonymous"></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>

3. Live example at https://www.jslint.com/jslint_wrapper_codemirror.html

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.:
     • save jslint.mjs, jslint_wrapper_vim.vim to directory ~/vimfiles/
     • vim-command :source ~/vimfiles/jslint_wrapper_vim.vim
3. Vim can now jslint files (via nodejs):
   • with vim-command :SaveAndJslint
   • with vim-key-combo <Ctrl-S> <Ctrl-J>

• 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
3. In VSCode, to autofix whitespace in file:
   • right-click context-menu and select [JSLint - Autofix Whitespace]
   • or use key-binding [Ctrl + Shift + J], [A]
   • or use key-binding [Cmd + Shift + J], [A] for Mac

• 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

• https://www.jslint.com/apidoc.html

Directive

/*jslint*/

• /*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.

String(0 | 1);

• /*jslint browser*/

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

localStorage.getItem("foo");

• /*jslint convert*/

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

String(new Date() + "");
String(!!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.

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

String(
  "hello"
);

• /*jslint long*/

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

String("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa");

• /*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.

String('hello');

• /*jslint subscript*/

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

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

• /*jslint this*/

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

function foo() {
    return this;
}
foo();

• /*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 variable*/

/*jslint variable*/
// Allow unordered const and let declarations not at top of function-scope.

let aa = "hello";
String(aa);
let bb = "goodbye";
String(bb);

• /*jslint white*/

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

String(
"hello"
);

/*global*/

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

foo();
bar();

/*property*/

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

String({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

• https://github.com/tc39/proposals/blob/main/finished-proposals.md
• https://github.com/lukehoban/es6features

Package Listing

Changelog

• Full CHANGELOG.md

License

• JSLint is under Unlicense License.
• CodeMirror editor is under MIT License.
• Function v8CoverageListMerge is derived from MIT Licensed v8-coverage.

Devops Instruction

pull-request merge

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

   • latest nodejs-lts version @ https://nodejs.org/en/about/previous-releases

2. update CHANGELOG.md

   • copy recent <commit entries> to <CHANGELOG.md entries> ordered by impact
   • run

     # re-run until version propagates
     npm run test2
     
     # re-run until version propagates
     sh jslint_ci.sh shGithubPrCreate alpha beta # v20yy.mm.dd __pr_beta_pre
     
     git push upstream alpha -f
     

     • verify ci-success @ https://github.com/kaizhu256/jslint/actions
     • verify ci-success @ https://github.com/jslint-org/jslint/actions

3. goto https://github.com/jslint-org/jslint/compare/beta...kaizhu256:jslint:branch-p20yy.mm.dd

   • 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
     • verify ci-success @ https://github.com/jslint-org/jslint/actions/workflows/on_pull_request.yml

4. wait awhile before continuing ...

   • click Squash and merge
     • verify ci-success @ https://github.com/jslint-org/jslint/actions
   • run

     sh jslint_ci.sh shGithubPrCleanup
     
     git push upstream alpha -f
     

     • verify ci-success @ https://github.com/kaizhu256/jslint/actions
     • verify ci-success @ https://github.com/jslint-org/jslint/actions
   • click Delete branch

branch-master commit

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

   • latest nodejs-lts version @ https://nodejs.org/en/about/previous-releases

2. update CHANGELOG.md

   • verify <CHANGELOG.md entries> ordered by impact
   • run

     # re-run until version propagates
     npm run test2
     
     # re-run until version propagates
     sh jslint_ci.sh shGithubPrCreate alpha master # v20yy.mm.dd __pr_master_pre
     
     git push upstream alpha -f
     

     • verify ci-success @ https://github.com/kaizhu256/jslint/actions
     • verify ci-success @ https://github.com/jslint-org/jslint/actions

3. goto https://github.com/jslint-org/jslint/compare/beta...kaizhu256:jslint:branch-v20yy.mm.dd

   • click Create pull request
   • input Add a title * with: # v20yy.mm.dd
   • input Add a description with:

     <CHANGELOG.md entry #1>
     <CHANGELOG.md entry extra>
     

   • click Preview and review
   • verify:
     • base respository: jslint-org/jslint
     • base: beta
   • click Create pull request
     • verify ci-success @ https://github.com/jslint-org/jslint/actions/workflows/on_pull_request.yml

4. wait awhile before continuing ...

   • click Squash and merge
     • verify ci-success @ https://github.com/jslint-org/jslint/actions
   • run

     sh jslint_ci.sh shGithubPrCleanup
     
     git push upstream alpha -f
     

     • verify ci-success @ https://github.com/kaizhu256/jslint/actions
     • verify ci-success @ https://github.com/jslint-org/jslint/actions
   • click Delete branch
   • run

     git push origin beta:master
     
     git push upstream beta:master
     

     • verify ci-success @ https://github.com/kaizhu256/jslint/actions
     • verify ci-success @ https://github.com/jslint-org/jslint/actions

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. • run

     git push upstream beta:master
     

     • verify ci-success @ https://github.com/jslint-org/jslint/actions
3. 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
     • verify ci-success @ https://github.com/jslint-org/jslint/actions
     • verify email-notification Successfully published @jslint-org/jslint@20yy.mm.dd

vscode-jslint qa

# build vscode-jslint
sh jslint_ci.sh shCiVscePackageJslintWrapperVscode

# open vscode and debug
code \
    --disable-extensions \
    --extensionDevelopmentPath=\
'C:\Users\<username>\Documents\jslint\.artifact\jslint_wrapper_vscode'

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