eslint-plugin-erb

Lint your JavaScript code inside ERB files (.js.erb). A zero-dependency plugin for ESLint.
Also lints your HTML code in .html.erb if you want to.

Usage

Install

Install the plugin alongside ESLint:

npm install --save-dev eslint eslint-plugin-erb

Configure

Starting of v9 ESLint provides a new flat config format (eslint.config.js). Also see the configuration migration guide. Use it as follows and it will automatically lint all your JavaScript code in .js.erb files:

// eslint.config.js
import erb from "eslint-plugin-erb";

export default [
  erb.configs.recommended,
  {
    linterOptions: {
      // The "unused disable directive" is set to "warn" by default.
      // For the ERB plugin to work correctly, you must disable
      // this directive to avoid issues described here
      // https://github.com/eslint/eslint/discussions/18114
      // If you're using the CLI, you might also use the following flag:
      // --report-unused-disable-directives-severity=off
      reportUnusedDisableDirectives: "off",
    },
    // your other configuration options
  }
];

See more complete example

// eslint.config.js
import js from "@eslint/js";
import stylistic from "@stylistic/eslint-plugin";
import globals from "globals";
import erb from "eslint-plugin-erb";

const customizedStylistic = stylistic.configs.customize({
  "indent": 2,
  "jsx": false,
  "quote-props": "always",
  "semi": "always",
  "brace-style": "1tbs",
});

const customGlobals = {
  MyGlobalVariableOrFunctionOrClassOrWhatever: "readable",
};

// [1] https://eslint.org/docs/latest/use/configure/configuration-files-new#globally-ignoring-files-with-ignores

export default [
  js.configs.recommended,
  erb.configs.recommended,
  // Globally ignoring the following files
  // "Note that only global ignores patterns can match directories.
  // 'ignores' patterns that are specific to a configuration will
  // only match file names." ~ see [1]
  {
    ignores: [
      "node_modules/",
      "tests/fixtures/",
      "tmp/",
    ],
  },
  {
    plugins: {
      "@stylistic": stylistic,
    },
    rules: {
      ...customizedStylistic.rules,
      "no-unused-vars": ["warn", { argsIgnorePattern: "^_" }],
      "@stylistic/quotes": ["error", "double", { avoidEscape: true }],
    },
    languageOptions: {
      ecmaVersion: 2022,
      sourceType: "module",
      globals: {
        ...customGlobals,
        ...globals.browser,
        ...globals.node,
      },
    },
    linterOptions: {
      // The "unused disable directive" is set to "warn" by default.
      // For the ERB plugin to work correctly, you must disable
      // this directive to avoid issues described here
      // https://github.com/eslint/eslint/discussions/18114
      // If you're using the CLI, you might also use the following flag:
      // --report-unused-disable-directives-severity=off
      reportUnusedDisableDirectives: "off",
    },
  },
];

Alternative way to configure the processor

With this variant you have a bit more control over what is going on, e.g. you could name your files .js.special-erb and still lint them (if they contain JS and ERB syntax).

// eslint.config.js
import erb from "eslint-plugin-erb";

export default [
  {
    files: ["**/*.js.erb"],
    processor: erb.processors.processorJs,
  },
  {
    linterOptions: {
      // The "unused disable directive" is set to "warn" by default.
      // For the ERB plugin to work correctly, you must disable
      // this directive to avoid issues described here
      // https://github.com/eslint/eslint/discussions/18114
      // If you're using the CLI, you might also use the following flag:
      // --report-unused-disable-directives-severity=off
      reportUnusedDisableDirectives: "off",
    },
    // your other configuration options
  }
];

Legacy: you can still use the old `.eslintrc.js` format

You can extend the plugin:erb/recommended-legacy config that will enable the ERB processor on all .js.erb files.

// .eslintrc.js
module.exports = {
    extends: "plugin:erb/recommended-legacy"
};

Or you can configure the processor manually:

// .eslintrc.js
module.exports = {
    plugins: ["erb"],
    overrides: [
        {
            files: ["**/*.js.erb"],
            processor: "erb/processorJs"
        }
    ]
};

If you also want to lint HTML code in .html.erb files, you can use our preprocessor in conjunction with the amazing html-eslint plugin. Install html-eslint, then add the following to your ESLint config file (flat config format):

// eslint.config.js
import erb from "eslint-plugin-erb";

export default [
  // your other configurations...
  {
    processor: erb.processors["processorHtml"],
    ...html.configs["flat/recommended"],
    files: ["**/*.html", "**/*.html.erb"],
    rules: {
        ...html.configs["flat/recommended"].rules,
        "@html-eslint/indent": ["error", 2],
        // other rules...
    },
  }
];

Additionally, you might want to add the following option to the other objects ({}) in export default [] (at the same level like the files key above), since other rules might be incompatible with HTML files:

ignores: ["**/*.html**"],

Editor Integrations

The ESLint extension for VSCode has built-in support for the ERB processor once you've configured it in your .eslintrc.js file as shown above.

If you're using VSCode, you may find this settings.json options useful:

{
    "editor.formatOnSave": false, // it still autosaves with the options below
    //////////////////////////////////////
    // JS (ESLint)
    //////////////////////////////////////
    // https://eslint.style/guide/faq#how-to-auto-format-on-save
    // https://github.com/microsoft/vscode-eslint#settings-options
    "eslint.format.enable": true,
    "[javascript]": {
        "editor.formatOnSave": false, // to avoid formatting twice (ESLint + VSCode)
        "editor.defaultFormatter": "dbaeumer.vscode-eslint" // use ESLint plugin
    },
    "editor.codeActionsOnSave": {
        "source.fixAll.eslint": "explicit" // Auto-fix ESLint errors on save
    },
    // this disables VSCode built-int formatter (instead we want to use ESLint)
    "javascript.validate.enable": false,
    //////////////////////////////////////
    // Files
    //////////////////////////////////////
    "files.associations": {
        "*.js.erb": "javascript"
    },
}

Limitations

• Does not account for code indentation inside if/else ERB statements, e.g. this snippet

<% if you_feel_lucky %>
    console.log("You are lucky 🍀");
<% end %>

will be autofixed to

<% if you_feel_lucky %>
console.log("You are lucky 🍀");
<% end %>

• No support for ESLint suggestions (but full support for autofixes as shown in the GIF above)