JSLint, The JavaScript Code Quality and Coverage Tool

Douglas Crockford douglas@crockford.com

Status

Branch	master (v2024.6.28)	beta (Web Demo)	alpha (Development)
CI
Coverage
Demo
Artifacts

Table of Contents

1. Web Demo

2. Web Demo Archived

3. 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:

4. Quickstart JSLint Report

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

5. 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:

6. Quickstart JSLint in CodeMirror

7. Quickstart JSLint in Vim

8. Quickstart JSLint in VSCode

9. Documentation

   • API Doc
   • Directive /*jslint*/
     • /*jslint beta*/
     • /*jslint bitwise*/
     • /*jslint browser*/
     • /*jslint convert*/
     • /*jslint couch*/
     • /*jslint devel*/
     • /*jslint eval*/
     • /*jslint fart*/
     • /*jslint for*/
     • /*jslint getset*/
     • /*jslint indent2*/
     • /*jslint long*/
     • /*jslint node*/
     • /*jslint nomen*/
     • /*jslint single*/
     • /*jslint subscript*/
     • /*jslint this*/
     • /*jslint trace*/
     • /*jslint unordered*/
     • /*jslint white*/
   • Directive /*global*/
   • Directive /*property*/
   • Directive /*jslint-disable*/.../*jslint-enable*/
   • Directive //jslint-ignore-line

10. Package Listing

11. Changelog

12. License

13. Devops Instruction

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

Web Demo

• https://www.jslint.com

Web Demo Archived

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

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 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 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=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 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=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 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/5.65.10/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://codemirror.net/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>

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

• 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.

JSLint can be run anywhere that JavaScript (or Java) can run.

The place to express yourself in programming is in the quality of your ideas and the efficiency of their execution. The role of style in programming is the same as in literature: It makes for better reading. A great writer doesn't express herself by putting the spaces before her commas instead of after, or by putting extra spaces inside her parentheses. A great writer will slavishly conform to some rules of style, and that in no way constrains her power to express herself creatively. See for example William Strunk's The Elements of Style [https://www.crockford.com/style.html].

This applies to programming as well. Conforming to a consistent style improves readability, and frees you to express yourself in ways that matter. JSLint here plays the part of a stern but benevolent editor, helping you to get the style right so that you can focus your creative energy where it is most needed.

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.

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;

Directive /*global*/

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

foo();
bar();

Directive /*property*/

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

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

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

/*jslint-disable*/

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

/*jslint-enable*/

Directive //jslint-ignore-line

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

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

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

• find highest issue-number at https://github.com/jslint-org/jslint/issues/, https://github.com/jslint-org/jslint/pulls/, and add +1 to it for PR-xxx
• shGitPullrequest beta beta
  • verify ci-success for origin-branch-alpha
  • https://github.com/kaizhu256/jslint/actions
• git push upstream alpha -f
  • verify ci-success for upstream-branch-alpha
  • https://github.com/jslint-org/jslint/actions
• goto https://github.com/jslint-org/jslint/compare/beta...kaizhu256:jslint:branch-p2024.11.9
• click Create pull request
• input Add your description here... with:

Fixes #xxx.
- <primary-commit-message>

This PR will ...

This PR will additionally:
- <secondary-commit-message>
...

<screenshot>

• verify commit into jslint-org:beta
• click Create pull request
  • verify ci-success for pull-request
  • https://github.com/jslint-org/jslint/actions/workflows/on_pull_request.yml
• wait awhile before continuing ...
• click Rebase and merge
  • verify ci-success for upstream-branch-beta
  • https://github.com/jslint-org/jslint/actions
• shGitPullrequestCleanup
  • verify ci-success for origin-branch-alpha
  • https://github.com/kaizhu256/jslint/actions
• git push upstream alpha -f
  • verify ci-success for upstream-branch-alpha
  • https://github.com/jslint-org/jslint/actions
• click Delete branch

branch-master commit

• shGitPullrequest master beta
  • verify ci-success for origin-branch-alpha
  • https://github.com/kaizhu256/jslint/actions
• git push upstream alpha -f
  • verify ci-success for upstream-branch-alpha
  • https://github.com/jslint-org/jslint/actions
• goto https://github.com/jslint-org/jslint/compare/beta...kaizhu256:jslint:branch-v2024.6.28
• click Create pull request
• input Add a title with: # v20yy.mm.dd
• input Add a description with:

- <primary-commit-message>
- <secondary-commit-message>

• verify commit into jslint-org:beta
• click Create pull request
  • verify ci-success for pull-request
  • https://github.com/jslint-org/jslint/actions/workflows/on_pull_request.yml
• wait awhile before continuing ...
• click Rebase and merge
  • verify ci-success for upstream-branch-beta
  • https://github.com/jslint-org/jslint/actions
• shGitPullrequestCleanup
  • verify ci-success for origin-branch-alpha
  • https://github.com/kaizhu256/jslint/actions
• git push upstream alpha -f
  • verify ci-success for upstream-branch-alpha
  • https://github.com/jslint-org/jslint/actions
• click Delete branch
• git push origin beta:master
  • verify ci-success for origin-branch-master
  • https://github.com/kaizhu256/jslint/actions
• git push upstream beta:master
  • verify ci-success for upstream-branch-master
  • https://github.com/jslint-org/jslint/actions

branch-master publish

• git push upstream beta:master
  • verify ci-success for upstream-branch-master
  • https://github.com/jslint-org/jslint/actions
• goto https://github.com/jslint-org/jslint/releases/new
• input Choose a tag with: v20yy.mm.dd
• click Create new tag: v20yy.mm.dd on publish
  • verify correct-year 20yy
• select Target: master
• select Previous tag:auto
• input Release title with: v20yy.mm.dd - <primary-commit-message>
• input Describe this release with:

- <primary-commit-message>
- <secondary-commit-message>

• click Generate release notes
• click Set as the latest release
• click Preview and review
• click Publish release
  • verify ci-success for upstream-branch-publish
  • https://github.com/jslint-org/jslint/actions
  • verify email-notification Successfully published @jslint-org/jslint@20yy.mm.dd

vscode-jslint publish

• 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
• goto https://marketplace.visualstudio.com/manage/publishers/jslint
• right-click Update
• upload downloaded file vscode-jslint-20yy.mm.dd.vsix
• click 'Upload'
• verify email-notification [Succeeded] Extension publish on Visual Studio Marketplace - vscode-jslint