Code Linting for nodes

Hi all, just a quick hint for anyone writing custom nodes.

I use the ESLINT tool which integrates with VSCode in order to dynamically spot loads of coding issues as well as to help enforce a particular coding style (which makes later bugfixes, review and updates much easier).

Unfortunately, I recently found a fairly critical issue with ESLINT when working with node.js and that meant that I always ended up with spurious "errors" being listed that weren't correct. The issue is that node.js has supported some advanced JavaScript features for a few years before they were finally ratified in an ECMA standard. Notably Public Class Variables.

Of course, as a good open source citizen, I raised these with the eslint project and got back some very unhelpful responses. Fortunately though, a collaborator on that project responded with a helpful comment.

you can check out the plugin eslint-plugin-n. it has a rule for such a purpose:

also, eslint-plugin-es can be helpful.

So I thought I'd pass that along for everyone else as well. :grinning:

1 Like

And for anyone who might want the config that I'm using for ESLINT - this is the current one (and hopefully the last since I've seriously lost track of how many different versions I've tried over the last few years.

Please note that this config ONLY works for the runtime of your custom nodes. It will not play nicely with the html file that is loaded into the Editor. I now have my editor panel source code in a separate src folder in 4 parts to make it a lot easier to code. That folder has a different eslint config.

Also note that this config assumes node.js v12 LTS right now which matches the current Node-RED v2 minimum version. When Node-RED v3 comes out, I'll be updating my configs to use Node.js v14 LTS. As you can see, that will open up a bunch of new JavaScript capabilities, some of which are really useful such as private class methods and others will make code shorter such as optional chaining. Node.js v14 will also finally start to bring together node.js's full support for ECMA Modules which should make migration a tiny bit easier.

/** JavaScript Versions
 *  5 is minimum -> Last IE11
 *  6 = 2015 -> Node >8.10, iOS12+
 *  7 = 2016 -> FF78+,
 *  8 = 2017 -> Node 10.9+
 *  9 = 2018 -> Node 12.11+
 * 10 = 2019 -> Node 12.20 LTS
 * 11 = 2020 -> Node 14 LTS
 * 12 = 2021 -> Node 16
/** Node.js supports (
 * v07 - async/await
 * v09 - tagged template literals with invalid escape sequences,  RegExp lookbehind assertions
 * v10 - optional catch binding (no need for err param on catch), BigInt, import.meta,
 *         RegExp Unicode property escape sequences \p{...},
 *         trimStart/trimEnd, async iteration, Promise.prototype.finally,
 *         RegExp named capture groups
 * v11 - Array.prototype.{flat,flatMap}, Symbol.prototype.description
 * v12 - Promise.allSettled, globalThis, numeric separators, Object.fromEntries
 * v13 - import (modules), dynamic import(), export
 * v14 - optional chaining, Nullish Coalescing operators, String.prototype.matchAll,
 *         Intl.DisplayNames, Intl.DateTimeFormat, Async Local Storage, Top-Level Await, Diagnostic report,
 *         WeakReferences, private class methods
 * v15 - logical assignment operators, String.prototype.replaceAll, Promise.any, AggregateError, AbortController,
 *        Promisified setTimeout/setImmediate
module.exports = {
    env: {
        browser: false,
        commonjs: true,
        jquery: false,
        node: true,
        // es2019: true,
        'shared-node-browser': false
    parserOptions: {
        // Only ESLint 6.2.0 and later support ES2020. Node.js v12+ supports some things only ratified in 2020
        'ecmaVersion': 2022,
        sourceType: 'script'
    root: true,
    globals: {
        Set: true, // Not sure why eslint doesn't recognise this as it is part of node.js since v0.12
        RED: true,
    overrides: [
            files: ['*.mod.js', '*.mjs'],
            parserOptions: { sourceType: 'module' },
    plugins: [
        'html',     // Check scripts in HTML.
        'es',       // Help avoid js that is too new.
        'jsdoc',    // JSDoc.
        'promise',  // Better promises.
        'sonarjs'   // Detect bugs and suspicious patterns.
        // 'prettier', //
    extends: [
        // The n plugin reads the min. node.js version from package.json and error's any ES features not available in that version.
    rules: {
        'n/no-process-exit': 'error',

        // remove once min engines moves to node.js v14+
        'es/no-optional-chaining': 'error',
        'es/no-dynamic-import': 'error',
        'es/no-nullish-coalescing-operators': 'error',
        // remove once min engines moves to node.js v15+
        'es/no-logical-assignment-operators': 'error',
        'es/no-promise-any': 'error',
        'es/no-numeric-separators': 'error',

        // Tidy up some jsdoc oddities
        'jsdoc/multiline-blocks': 0,
        'jsdoc/newline-after-description': 0,
        'jsdoc/no-multi-asterisks': 0,
        'jsdoc/tag-lines': 0,
        'jsdoc/valid-types': 0, // Rubbish, fails on common type configs
        // @ts-ignore
        'jsdoc/no-undefined-types': 0, // ['error'|'warn', {'definedTypes':['Promise']}],

        // Try to keep code complexity in functions to a minimum
        'sonarjs/cognitive-complexity': ['error', 60],  // default is 15! Need to try and improve this :-)

        // Make Standard less annoying
        'brace-style': 'off',     // You should only use one-true-brace style but sometimes we want to compress things a bit.
        'comma-dangle': 'off',    // Lack of dangles wastes soo much time correcting lists
        'dot-notation': 'off',    // Turn off to allow for tslint's brain-dead treatment of expando objects in JS
        'indent': ['error', 4, { 'SwitchCase': 1 }],   // Standard wants 2, I like 4
        'space-before-function-paren': 'off', // No, don't need space between fn and arg!
        'no-multi-spaces': 'off', // Readability is more important than size (reduce size using uglify)
        'object-shorthand': ['error', 'consistent'],
        'padded-blocks': 'off',   // Sometimes you just need some space! See above.
        'space-in-parens': 'off', // Sometimes you just need some space!
        'spaced-comment': ['error', 'always', {
            'markers': ['html', '#region', '#endregion']
        'quote-props': 'off',     // Sometimes it is necessary and then much nicer to be able to quote things that don't need it.