mysticatea/eslint-plugin-es

ESLint plugin about ECMAScript syntactic features.

eslint-plugin-es

ESLint plugin which disallows each ECMAScript syntax.

🏁 Goal

Espree, the default parser of ESLint, has supported ecmaVersion option. However, the error messages of new syntax are not readable (e.g., "unexpected token" or something like).

When we use this plugin along with the latest ecmaVersion option value, it tells us the readable error message for the new syntax, such as "ES2020 BigInt is forbidden." Plus, this plugin lets us disable each syntactic feature individually.

📖 Usage

See documentation

🚥 Semantic Versioning Policy

This plugin follows semantic versioning and ESLint's semantic versioning policy.

• We will release a new minor version to add new rules when TC39 decided to advance proposals to Stage 4. In the minor releases, we don't update configs.
• We will release a new major version to update configs when new ECMAScript snapshots are available.

📰 Changelog

See releases.

❤️ Contributing

Welcome contributing!

Please use GitHub's Issues/PRs.

Development Tools

• npm test runs tests and measures coverage.
• npm run clean removes the coverage result of npm test command.
• npm run coverage shows the coverage result of the last npm test command.
• npm run docs:build builds documentation.
• npm run docs:watch builds documentation on each file change.
• npm run watch runs tests on each file change.

eslint-plugin-es's Issues

Incorporate browser compatibility data

Rather than banning particular ES versions or individual features, I'd like to be able to declare the browser features that are to be supported. This might be for this plugin, or some companion plugin/config that works with it.

As a starting idea...

// .eslinrc.json
{
  "plugins": ["es"],
  "extends": "plugin:es/browserslist"
}

// .browserslistrc
last 3 versions

The es/no-foo rules included in the output config would be dynamic, based on the browsers matching the browserslist spec, looked up against a compatibility database.

Leading on from:

• sindresorhus/project-ideas#103
• https://github.com/robatwilliams/workie (see bottom of readme for links to compat data)

Object.create is missed in rules

New Rule Proposal: `no-object-hasown`

Please describe what the rule should do:

Disallow Object.hasOwn method.

This method will be added in ES2022.

https://github.com/tc39/proposal-accessible-object-hasownproperty

Provide 2-3 code examples that this rule will warn about:

if (Object.hasOwn(object, "foo")) {
  // ...
}

no-atomics and no-shared-array-buffer not working

Hi :)

I've configured these 4 rules:
'es/no-atomics': 'error', 'es/no-shared-array-buffer': 'error', 'es/no-regexp-lookbehind-assertions': 'error', 'es/no-export-ns-from': 'error',

no-atomics and no-shared-array-buffer are not working.

This code snippet:
`const sab = new SharedArrayBuffer(1024);
const ta = new Uint8Array(sab);

	ta[0] = 5; // 5

	Atomics.add(ta, 0, 12); // 5
	// eslint-disable-next-line no-undef
	Atomics.load(ta, 0); // 17`

eslint (v7.32) doesn't prevent it from using. It says 'no-undef', and if adding this exception, everything is ok...

Rule missing for padding features ES8 / ECMA2017

Hi :)

I'm missing rules for e.g. padStart and padEnd in ES8/ECMA2017

Support ESLint 8.x

ESLint v8.0.0 is released 🎉

It would be awesome to have official ESLint 8 support. 👊
I'm happy to help where I can of course 🙂

Create rule for "Obect.fromEntries"

From http://www.ecma-international.org/ecma-262/10.0/index.html:

This specification, the 10th edition, introduces a few new built-in functions: flat and flatMap on Array.prototype for flattening arrays, Object.fromEntries for directly turning the return value of Object.entries into a new Object, ...

Update changelog / add release for 2.0.0

The README states that one should check GitHub releases to find out what has changed in a release: https://github.com/mysticatea/eslint-plugin-es#-changelog

But there are no release notes written for 2.0.0, so unless one looks at the commits there are no way to find out what motivated the major bump in version number. (A written release can also get picked up by tools like Renovate)

Is there a rule for the Array.prototype.flat feature?

Hi :)

I'm missing a rule for the flat feature. Either I can't find it or there is no?
It should be part of the ES2019 set?

Other features from ES2019 are missing too?

Type Error: cannot read 'length' of undefined.

Tell us about your environment

• ESLint Version: 5.1.0
• Node Version: 8.11.3
• npm Version: 6.1.0
• yarn Version: 1.7.0

What parser (default, Babel-ESLint, etc.) are you using?
babel-eslint

Please show your full configuration:

Configuration

module.exports = {
	"parser": "babel-eslint",
	"root": true,
	"plugins": [
		"node",
		"flowtype"
	],
	"extends": ["eslint:recommended", "plugin:node/recommended"],
	"env": {
		"node": true,
		"es6": true,
		"jest": true
	},
	"parserOptions": { "ecmaVersion": 2017, "sourceType": "module"},
	"rules": {
		"no-useless-escape": "off",
		"quote-props": ["error", "as-needed"],
		"no-dupe-keys": "error",
		"quotes": ["error", "double"],
		"no-undef": "error",
		"no-extra-semi": "error",
		"semi": "error",
		"no-template-curly-in-string": "error",
		"no-caller": "error",
		"yoda": "error",
		"eqeqeq": "error",
		"global-require": "off",
		"brace-style": "error",
		"key-spacing": "error",
		"space-in-parens": ["error", "never"],
		"space-infix-ops": "error",
		"indent": ["error", "tab", { "SwitchCase": 1 }],
		"no-extra-bind": "warn",
		"no-empty": "off",
		"no-multiple-empty-lines": "error",
		"no-multi-spaces": "error",
		"no-process-exit": "off",
		"no-trailing-spaces": "error",
		"no-use-before-define": "off",
		"no-unused-vars": ["error", { "args": "none" }],
		"no-unsafe-negation": "error",
		"no-loop-func": "warn",
		"space-before-function-paren": ["error", "never"],
		"space-before-blocks": "error",
		"object-curly-spacing": ["error", "always"],
		"object-curly-newline": ["error", { "consistent": true }],
		"keyword-spacing": ["error", {
			"after": true,
			"overrides": {
				"const": { "after": true },
				"try": { "after": true },
				"throw": { "after": true },
				"case": { "after": true },
				"return": { "after": true },
				"finally": { "after": true },
				"do": { "after": true }
			}
		}],
		"no-console": "off",
		"valid-jsdoc": "error",
		"node/no-unsupported-features": 'off',
		"node/no-deprecated-api": "error",
		"node/no-missing-import": "error",
		"node/no-extraneous-require": ["error"],
		"eol-last": ["error", "always"],
		"newline-per-chained-call": "off",
		"node/process-exit-as-throw": "error"
	},
	"settings": {
    "flowtype": {
      "onlyFilesWithFlowAnnotation": true
    }
  }
};

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

eslint src/

What did you expect to happen?
Throw eslint errors or succeed.

What actually happened? Please include the actual, raw output from ESLint.

I see this error:

Cannot read property 'length' of undefined
TypeError: Cannot read property 'length' of undefined
    at :function (project/node_modules/eslint-plugin-es/lib/rules/no-trailing-function-commas.js:30:44)
    at listeners.(anonymous function).forEach.listener (project/node_modules/eslint/lib/util/safe-emitter.js:45:58)
    at Array.forEach (<anonymous>)
    at Object.emit (project/node_modules/eslint/lib/util/safe-emitter.js:45:38)
    at NodeEventGenerator.applySelector (project/node_modules/eslint/lib/util/node-event-generator.js:251:26)
    at NodeEventGenerator.applySelectors (project/node_modules/eslint/lib/util/node-event-generator.js:278:22)
    at NodeEventGenerator.enterNode (project/node_modules/eslint/lib/util/node-event-generator.js:294:14)
    at CodePathAnalyzer.enterNode (project/node_modules/eslint/lib/code-path-analysis/code-path-analyzer.js:632:23)
    at nodeQueue.forEach.traversalInfo (project/node_modules/eslint/lib/linter.js:861:28)
    at Array.forEach (<anonymous>)
error Command failed with exit code 2.

Since the error was thrown by this package, i thought it would be better to post it here other than on eslint, if it is better to be there, just let me know than i will move it.

Thanks.

Add a TypeScript preset to turn off rules that the tsc compiler correctly transpiles

At the moment, we're using one of the restrict-to-esNNNN presets, which are really great. However, when using TypeScript, there are a lot of things that tsc transpiles correctly regardless of target, so we end up "canceling" a set of rules that are perfectly fine with TypeScript:

## ES2020

# Disallow nullish coalescing operators
# https://eslint-plugin-es.mysticatea.dev/rules/no-nullish-coalescing-operators.html
# This is correctly transpiled by TypeScript
es/no-nullish-coalescing-operators: off

# Disallow optional chaining
# https://eslint-plugin-es.mysticatea.dev/rules/no-optional-chaining.html
# This is correctly transpiled by TypeScript
es/no-optional-chaining: off

## ES2019

# Disallow optional catch binding
# https://eslint-plugin-es.mysticatea.dev/rules/no-optional-catch-binding.html
# This is correctly transpiled by TypeScript
es/no-optional-catch-binding: off

## ES2018

# Disallow async iteration
# https://eslint-plugin-es.mysticatea.dev/rules/no-async-iteration.html
# This is correctly transpiled by TypeScript
es/no-async-iteration: off

# Disallow rest/spread properties
# https://eslint-plugin-es.mysticatea.dev/rules/no-rest-spread-properties.html
# This is correctly transpiled by TypeScript
es/no-rest-spread-properties: off

## ES2017

# Disallow async function declarations
# https://eslint-plugin-es.mysticatea.dev/rules/no-async-functions.html
# This is correctly transpiled by TypeScript
es/no-async-functions: off

# Disallow trailing commas in parameter/argument lists
# https://eslint-plugin-es.mysticatea.dev/rules/no-trailing-function-commas.html
# This is correctly transpiled by TypeScript
es/no-trailing-function-commas: off

It would be really nice if there was an extra preset to load at the end that cancels those rule correctly, similarly to how eslint-config-prettier turns off all rules that are unnecessary:

extends:
  - plugin:es/restrict-to-es2015
  - plugin:es/typescript

New Rule Proposal: `no-private-fields-in-in`

Please describe what the rule should do:

Disallows #x in obj syntax added in ES2022.

https://github.com/tc39/proposal-private-fields-in-in

Provide 2-3 code examples that this rule will warn about:

class C {
  #brand;

  static isC(obj) {
    return #brand in obj; // <-
  }
}

New Rule Proposal: `no-regexp-d-flag`

Please describe what the rule should do:

Disallows RegExp d flag added in ES2022.

https://github.com/tc39/proposal-regexp-match-indices

Provide 2-3 code examples that this rule will warn about:

const re1 = /a+(?<Z>z)?/d;

/./d;

`no-arrow-functions` --fix incorrectly converts async functions

async () => {} is being automatically converted to synchronous functions by omitting the async before function(){}

Object.entries

Hi :)

In the rules.json I see:
"entries": { "compatible": true, "alternative": "Object.entries()", "ES6": true },

But I think Object.entries is not ES6/ECMA2015, it's ES8/ECMA2017

And it's also missing in this documentation?
https://www.npmjs.com/package/eslint-plugin-you-dont-need-lodash-underscore

New Rule Proposal: `no-top-level-await`

Please describe what the rule should do:

Disallows Top-level await added in ES2022.

https://github.com/tc39/proposal-top-level-await

Provide 2-3 code examples that this rule will warn about:

const strings = await import(`/i18n/${navigator.language}`);

const connection = await dbConnector();

let jQuery;
try {
  jQuery = await import('https://cdn-a.com/jQuery');
} catch {
  jQuery = await import('https://cdn-b.com/jQuery');
}

eslint-utils dependency vulnerability

eslint-utils has a vulnerability in versions >= 1.2.0, < 1.4.1

Can you update the version of the the eslint-utils dependency from 1.3.0 to at least 1.4.1 in package.json to fix it?

Add ES3 rules

Why? For some specific use cases, it could be useful to disable ALL ES built-ins. In my case, it's writing safe polyfills which don't use methods directly for preventing monkey-patching by something with observable effects.

New Rule Proposal: `no-class-fields`

Please describe what the rule should do:

Disallows Class Fields added in ES2022.

https://github.com/estree/estree/blob/master/es2022.md

Provide 2-3 code examples that this rule will warn about:

https://github.com/tc39/proposal-class-fields

class Counter  {
  x = 0;
}

https://github.com/tc39/proposal-private-methods

class Counter  {
  #xValue = 0;

  get #x() { return #xValue; }
  set #x(value) {
    this.#xValue = value;
    window.requestAnimationFrame(this.#render.bind(this));
  }

  #clicked() {
    this.#x++;
  }

  constructor() {
    super();
    this.onclick = this.#clicked.bind(this);
  }

  connectedCallback() { this.#render(); }

  #render() {
    this.textContent = this.#x.toString();
  }
}

https://github.com/tc39/proposal-static-class-features

class CustomDate {
  // ...
  static epoch = new CustomDate(0);
}

export class JSDOM {

  static async fromURL(url, options = {}) {
    return JSDOM.#finalizeFactoryCreated(new JSDOM(body, options), "fromURL");
  }

  static #finalizeFactoryCreated(jsdom, factoryName) {
    // ...
  }
}

New Rule Proposal: `no-class-static-block`

Please describe what the rule should do:

Disallow class static initialization blocks added in ES2022.

https://github.com/tc39/proposal-class-static-block

Provide 2-3 code examples that this rule will warn about:

class C {
  static {
    // ...
  }
}

Add higher es version presets to lower one

Lower version preset like no-es5 should include all higher version presets, for easier use.

Currently, if I want disable es5 syntax, I have to do

{
      extends: [
        'plugin:es/no-2020',
        'plugin:es/no-2019',
        'plugin:es/no-2018',
        'plugin:es/no-2017',
        'plugin:es/no-2016',
        'plugin:es/no-2015',
        'plugin:es/no-5',
      ],
}

seems silly, and if someday this plugin add no-2020(Update: we already has no-2020, but missing on website https://eslint-plugin-es.mysticatea.dev/#presets) no-2021, and I didn't update my config, 20202021 syntax will sneak in.

I suggest we include no-2015 in no-5, include no-2016 in no-2015, ..., so to disable es5, I can simply just extends: ['no-5'], for someone only want disable 2018, I suggest new preset no-{version}-only, like no-2018-only.

This will be a breaking change, if you don't want that, we can support this by adding some presets like no-5-above, no-2015-above.

Support ESLint 7.x

ESLint v7.0.0 is released 🎉

It would be awesome to have official ESLint 7 support. 👊
I'm happy to help where I can of course 🙂

Unicode property lists per Unicode v12

tc39/ecma262#1468

New Rule Proposal: `no-arbitrary-module-namespace-names`

Please describe what the rule should do:

Disallow arbitrary module namespace names, added in ES2022.

tc39/ecma262#2154

Provide 2-3 code examples that this rule will warn about:

export { foo as "str" }

import { "str" as foo } from "mod";

Add support for Promise.any + AggregateError

As the Promise.any proposal got finalized, it should be present in the list of ES2021 rules.

Autofix of es/no-logical-assignment-operators is wrong.

obj.foo ??= value

should be auto-fixed to

obj.foo ?? (obj.foo = value)

so the setter isn't called if short-circuited.

Should check newly RegExp Unicode Property Escapes

See acornjs/acorn#798.

New Rule Proposal: `no-hashbang`

Please describe what the rule should do:

no-hashbang rule that disallow Hashbang comments, added in ES2023.

https://github.com/tc39/proposal-hashbang

Provide 2-3 code examples that this rule will warn about:

#!/usr/bin/env node

// ... script

Webpack use wrong version espree

I'm not sure why Webpack uses espree with a wrong version for documentation.

Published package appears to be broken

Hi, I just installed [email protected] which is the latest according to npm.

simple .eslintrc.js config

...
plugins: [
    'es',
  ],
rules: {
  'es/no-bigint': 'error',
  'es/no-dynamic-import': 'error',
},
...

Running npx eslint . , I got random loads of errors, eg.

  1:1  error  Definition for rule 'es/no-export-ns-from' was not found                es/no-export-ns-from
  1:1  error  Definition for rule 'es/no-import-meta' was not found                   es/no-import-meta
  1:1  error  Definition for rule 'es/no-nullish-coalescing-operators' was not found  es/no-nullish-coalescing-operators

Examining ./node_modules/eslint-plugin-es/lib/index.js it doesn't appear any of these rules exist, they don't appear to be in /lib/rules either ?

FYI: typescript-eslint@v6 will remove parserServices.hasFullTypeInformation

👋 Hi! I'm one of the maintainers of typescript-eslint. We're getting ready to release a new v6 major version of the tooling, which includes some small breaking changes.

Coming over from typescript-eslint/typescript-eslint#7124: I see this repo contains references to hasFullTypeInformation. That property is something we've never recommended using (see that issue & typescript-eslint/typescript-eslint#7158). We recommend instead using ESLintUtils.getParserServices per https://typescript-eslint.io/developers/custom-rules#typed-rules.

If you really want to "progressively enhance" lint rules, parserServices.program will be null if type information isn't available. But we definitely recommend against that kind of rule behavior changing.

Overall, I'd suggest trying out typescript-eslint@v6 and making sure internal builds & downstream repos still compile & lint nicely with all the changes. Let me know if there's anything we can do to help with the v6 upgrade! 💖

es/no-promise-prototype-finally doesn't work

Hi, I'm using version 4.1.0.
I'm getting the following error when using es/no-promise-prototype-finally
1:1 error Definition for rule 'es/no-promise-prototype-finally' was not found es/no-promise-prototype-finally

This is my eslint config:

module.exports = {
  parserOptions: {
    ecmaVersion: 5
  },
  extends: [
    'eslint:recommended',
    'plugin:jest/recommended',
    'plugin:es/restrict-to-es5'
  ],
  plugins: [
    'jest',
    'es'
  ],
  rules: {
    'es/no-promise-prototype-finally': 2,
    'es/no-promise': 0,
  },
  env: {
    node: true,
    browser: true,
    'jest/globals': true
  },
  settings: {
    es: { aggressive: true }
  },
  globals: {
    Promise: true
  }
};

Any advice?

Feature request: Add config for typescript

Hello,

Thank you for the plugin.

I am using typescript with target=ES2017 option.

If I have:

const y = { ...x };
const re = /(?<!a)b/u;

It is transpiled:

const y = Object.assign({}, x);
const re = /(?<!a)b/u;

So, with typescript I can use spread operator, but not regexp lookback.
Your restrict-to-es2017 does not catch this.

My suggestion is to add configs for typescript that should disallow those features that are missing in respective ES version and not transpiled by typescript.

I think that typescript configs should include only regexp-related rules, but not sure.

Create optional rules for prototype methods

I found your comment at explaining why these aren't available at the moment: #2 (comment). While it is true that you will get some false positives, many of the methods have unique enough names that most of the time you won't, and the rare cases that do can be fixed with an inline exception.

I suggest creating these rules and put them in separate rule groups so they are not enabled by default, but can be used when users are happy to deal with the small number of false positives.

We have a similar set of rules for Wikipedia at https://github.com/wikimedia/eslint-config-wikimedia/tree/master/language and would like to be able to use this library instead, but the prototype method rules are important to us and catch lots of issues.

What's the difference between no spread elements and properties?

First: Thanks for this. It's great!

Neither of these rules have examples and I'm not clear on what the difference is:

• no-spread-elements:
  https://github.com/mysticatea/eslint-plugin-es/blob/master/docs/rules/no-spread-elements.md
• no-rest-spread-properties:
  https://github.com/mysticatea/eslint-plugin-es/blob/master/docs/rules/no-rest-spread-properties.md

What's the difference?

BigInt and Dynamic Imports

New Rule Proposal: `no-array-prototype-findlast-findlastindex`

Please describe what the rule should do:

no-array-prototype-findlast-findlastindex rule that disallow array.findLast() and array.findLastIndex(), added in ES2023.

https://github.com/tc39/proposal-array-find-from-last

Provide 2-3 code examples that this rule will warn about:

array.findLast(e => test(e))
array.findLastIndex(e => test(e))

New version

Hi, @mysticatea. The rules for prototype methods were added 7 months ago, but the new version was not published forcing us to use this plugin from GitHub. Maby already makes sense to publish it on NPM? -)

Definition for rule 'es/no-string-prototype-replaceall' was not found

When trying to use only the "es/no-string-prototype-replaceall": "error" rule, eslint reports that this rule is not available:
Definition for rule 'es/no-string-prototype-replaceall' was not found

.eslintrc.json:

{
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "ecmaVersion": 2021,
    "sourceType": "module",
    "project": "./tsconfig.json"
  },
  "plugins": ["@typescript-eslint", "es",
  "rules": {
    "es/no-string-prototype-replaceall": "error"
  }
}

I'm using "eslint-plugin-es": "^4.1.0",

When, as a test, using es/no-async-iteration instead of the replaceall rule, it works.

Is there anything else I need to configure to make checks only for this rule work?

doco has typos

https://mysticatea.github.io/eslint-plugin-es/rules/

The extends: "plugin:es/no-es2018" config enables the following rules.
should read
The extends: "plugin:es/no-2018" config enables the following rules.

The extends: "plugin:es/no-es2017" config enables the following rules.
should read
The extends: "plugin:es/no-2017" config enables the following rules.

etc.
they all give name no-es where the name should be no-

A rule to disallow Annex B features

The ECMAScript language syntax and semantics defined in this annex are required when the ECMAScript host is a web browser. The content of this annex is normative but optional if the ECMAScript host is not a web browser.
https://tc39.es/ecma262/#sec-additional-ecmascript-features-for-web-browsers

Features in Annex B are optional language features.
It's worthful if there is a rule to disallow those optional language features.

New Rule Proposal: `no-array-prototype-at` and `no-string-prototype-at`

Please describe what the rule should do:

• no-array-prototype-at ... Disallow Array.prototype.at and TypedArray .prototype.at method.
• no-string-prototype-at ... Disallow String.prototype.at method.

These methods will be added in ES2022.

https://github.com/tc39/proposal-relative-indexing-method

Provide 2-3 code examples that this rule will warn about:

var e = array.at(-1);
var e = typedArray.at(-1);
var c = string.at(-1);

---

Do you think we should rename the rule and to check both arrays and strings?

Invitation to move to official `eslint-community` org

We would love to have this repo added to the official @eslint-community organization on GitHub.

As you can read in the '@eslint-community GitHub organization' RFC, the goal of this new org is to have a place where community members can help ensure widely depended upon ESLint related packages stay up to date with newer ESLint releases and doesn't hold the wider community back without depending on one person's GitHub/npm account.

Since this plugin is really popular (1M+ download/week) & since it's currently unmaintained (the latest commit is almost 2y old & the latest interaction is almost 2y old as well), we'd love you —@mysticatea— to transfer this repo to a better home, so you're welcome to transfer this repository to the new org.

Add ES2021 support.

https://tc39.es/ecma262/

Add support for WeakRefs

As the proposal for WeakRefs got finalized as part of ES2021, a rule should be added to disallow its usage.