Angular ESLint

Monorepo for all the tooling which enables ESLint to lint Angular projects

This project is made possible thanks to the continued hard work going into https://github.com/typescript-eslint/typescript-eslint, and brilliant work on the original TSLint rule implementations in https://github.com/mgechev/codelyzer.

Quick Start with Angular and ESLint
Supported Angular CLI Versions
Usage with Nx Monorepos
Packages included in this project
Package Versions
Migrating an Angular CLI project from Codelyzer and TSLint
Notes on ESLint Configuration
Notes on Performance
Rules List

Quick Start with Angular and ESLint

In order to create a brand new Angular CLI workspace which uses ESLint instead of TSLint and Codelyzer, simply run the following commands:

# Install the Angular CLI and @angular-eslint/schematics globally however you want (e.g. npm, yarn, volta etc)

npm i -g @angular/cli @angular-devkit/{core,schematics} @angular-eslint/schematics

# Create a new Angular CLI workspace using the @angular-eslint/schematics collection (instead of the default)

ng new --collection=@angular-eslint/schematics

After you follow the interactive prompts the Angular CLI gives you, you have now created a TSLint and Codelyzer free workspace with ng lint all set up and ready to lint your source code and HTML templates using ESLint! 🚀

Read on to find out more about the project and some important things to bear in mind with configuration and performance.

Supported Angular CLI Versions

We support Angular CLI 10.1.0 and onwards, including Angular CLI 11.x. This range is also captured by our integration-tests package.

Why Angular `10.1.0`?

Angular 10.1.0 is significant because at version 10.0.0 the Angular Team switched to using project references and a tsconfig.base.json at the root of the project. This ultimately was deemed to be unsuccessful and in 10.1.0 they switched back to the original tsconfig.json without project references. Because angular-eslint and typescript-eslint care about your underlying TypeScript config, it is important that you are on the updated version which does not use project references.

The schematic will error if you try and run it when you still have a tsconfig.base.json.

As usual, the Angular Team provided an automatic migration for these changes as part of ng update, so for most people this change wasn't an issue. If you updated manually (which is highly discouraged), then it is possible you did not apply this critical change and will therefore run into the error with the schematic.

We recommend going back an running the automated migrations from ng update, or fixing things up manually as a last resort.

Please do not open issues related to unsupported versions of the Angular CLI.

Usage with Nx Monorepos

Nx leans on some, but not all of the packages from this project.

Specifically:

It does not use the builder to execute ESLint
It does not use the schematics to generate files and config, and is responsible for configuring ESLint via .eslintrc.json files in a way that makes sense for Nx workspaces.

We strongly recommend that you do not try and hand-craft setups with angular-eslint and Nx. It is easy to gets things wrong.

If using Angular CLI, use the angular-eslint tooling as instructed below
If using Nx, defer to the Nx tooling itself to configure things for you, it has been designed and tested specifically for this purpose.

Issues specific to Nx's support of Angular + ESLint should be filed on the Nx repo: https://github.com/nrwl/nx

Packages included in this project

Please follow the links below for the packages you care about.

@angular-eslint/builder - An Angular CLI Builder which is used to execute ESLint on your Angular projects using standard commands such as ng lint
@angular-eslint/eslint-plugin - An ESLint-specific plugin that contains rules which are specific to Angular projects. It can be combined with any other ESLint plugins in the normal way.
@angular-eslint/template-parser - An ESLint-specific parser which leverages the @angular/compiler to allow for custom ESLint rules to be written which assert things about your Angular templates.
@angular-eslint/eslint-plugin-template - An ESLint-specific plugin which, when used in conjunction with @angular-eslint/template-parser, allows for Angular template-specific linting rules to run.
@angular-eslint/schematics - Schematics which are used to add and update configuration files which are relevant for running ESLint on an Angular workspace.

Package Versions

All of the packages are published with the same version number to make it easier to coordinate both releases and installations.

We publish a canary release on every successful merge to master, so you never need to wait for a new stable version to make use of any updates.

The latest version under the latest tag is:

The latest version under the canary tag (latest commit to master) is:

(Note: The only exception to the automated publishes described above is when we are in the final phases of creating the next major version of the libraries - e.g. going from 1.x.x to 2.x.x. During these periods, we manually publish canary releases until we are happy with the release and promote it to latest.)

Migrating an Angular CLI project from Codelyzer and TSLint

We have some tooling to make this as automated as possible, but the reality is it will always be somewhat project-specific as to how much work will be involved in the migration.

Step 1 - Add relevant dependencies

The first step is to run the schematic to add @angular-eslint to your project:

ng add @angular-eslint/schematics

This will handle installing the latest version of all the relevant packages for you and adding them to the devDependencies of your package.json.

Step 2 - Run the `convert-tslint-to-eslint` schematic on a project

The next thing to do is consider which "project" you want to migrate to use ESLint. If you have a single application in your workspace you will likely have just a single entry in the projects configuration object within your angular.json file. If you have a projects/ directory in your workspace, you will have multiple entries in your projects configuration and you will need to chose which one you want to migrate using the convert-tslint-to-eslint schematic.

You can run it like so:

ng g @angular-eslint/schematics:convert-tslint-to-eslint {{YOUR_PROJECT_NAME_GOES_HERE}}

The schematic will do the following for you:

Read your chosen project's tslint.json and use it to CREATE a .eslintrc.json at the root of the specific project which extends from the root config (if you do not already have a root config, it will also add one automatically for you).
- The contents of this .eslintrc.json will be the closest possible equivalent to your tslint.json that the tooling can figure out.
- You will want to pay close attention to the terminal output of the schematic as it runs, because it will let you know if it couldn't find an appropriate converter for a TSLint rule, or if it has installed any additional ESLint plugins to help you match up your new setup with your old one.
UPDATE the project's architect configuration in the angular.json to such that the lint "target" will invoke ESLint instead of TSLint.
UPDATE any instances of tslint:disable comments that are located within your TypeScript source files to their ESLint equivalent.

Now when you run:

npx ng lint {{YOUR_PROJECT_NAME_GOES_HERE}}

...you are running ESLint on your project! 🎉

Step 3 - Remove root TSLint configuration and use only ESLint

Once you are happy with your ESLint setup, you simply need to remove the root-level tslint.json and potentially uninstall TSLint and any TSLint-related plugins/dependencies if your Angular CLI workspace is now no longer using TSLint at all.

Notes on ESLint Configuration

It's important to understand up front that using Angular with ESLint is actually an advanced/complex use-case because of the nature of the files involved:

Angular projects use TypeScript files for source code
Angular projects use a custom/extended form of HTML for templates (be they inline or external HTML files)

The thing is: ESLint understands neither of these things out of the box.

Fortunately, however, ESLint has clearly defined points of extensibility that we can leverage to make this all work.

For detailed information about ESLint plugins, parsers etc please review the official ESLint documentation: https://eslint.org

The key principal of our configuration required for Angular projects is that we need to run different blocks of configuration for different file types/extensions. In other words, we don't want the same rules to apply on TypeScript files that we do on HTML/inline-templates.

Therefore, the critical part of our configuration is the "overrides" array:

{
  "overrides": [
    /**
     * -----------------------------------------------------
     * TYPESCRIPT FILES (COMPONENTS, SERVICES ETC) (.ts)
     * -----------------------------------------------------
     */
    {
      "files": ["*.ts"],

      // ... applies a special processor to extract inline Component templates
      // and treat them like HTML files
      "extends": ["plugin:@angular-eslint/template/process-inline-templates"]

      // ... other config specific to TypeScript files
    },

    /**
     * -----------------------------------------------------
     * COMPONENT TEMPLATES
     * -----------------------------------------------------
     */
    {
      "files": ["*.html"],
      // ... config specific to Angular Component templates
    }
  ]
}

By setting up our config in this way, we have complete control over what rules etc apply to what file types and our separate concerns remain clearer and easier to maintain.

Seriously, move (mostly) all configuration into `overrides`

Even though you may be more familiar with including ESLint rules, plugins etc at the top level of your config object, we strongly recommend only really having overrides (and a couple of other things like ignorePatterns, root etc) at the top level and including all plugins, rules etc within the relevant block in the overrides array.

Anything you apply at the top level will apply to ALL files, and as we've said above there is a really strict separation of concerns between source code and templates in Angular projects, so it is very rare that things apply to all files.

Let's take a look at full (but minimal), manual example of a config file (although we recommend deferring to the schematics for automatic config generation whenever possible):

.eslintrc.json

{
  "root": true,
  "overrides": [
    {
      "files": ["*.ts"],
      "parserOptions": {
        "project": [
          "tsconfig.app.json",
          "tsconfig.spec.json",
          "e2e/tsconfig.json"
        ],
        "createDefaultProgram": true
      },
      "extends": [
        "plugin:@angular-eslint/recommended",
        // This is required if you use inline templates in Components
        "plugin:@angular-eslint/template/process-inline-templates"
      ],
      "rules": {
        /**
         * Any TypeScript source code (NOT TEMPLATE) related rules you wish to use/reconfigure over and above the
         * recommended set provided by the @angular-eslint project would go here.
         */
        "@angular-eslint/directive-selector": [
          "error",
          { "type": "attribute", "prefix": "app", "style": "camelCase" }
        ],
        "@angular-eslint/component-selector": [
          "error",
          { "type": "element", "prefix": "app", "style": "kebab-case" }
        ]
      }
    },
    {
      "files": ["*.html"],
      "extends": ["plugin:@angular-eslint/template/recommended"],
      "rules": {
        /**
         * Any template/HTML related rules you wish to use/reconfigure over and above the
         * recommended set provided by the @angular-eslint project would go here.
         */
      }
    }
  ]
}

If I wanted to include other source code related rules extends etc, such as extending from eslint:recommended, then I would include that in the "extends": [] within the *.ts override block, NOT the root of the config object.

Our schematics already do the "right" thing for you automatically in this regard, but if you have to configure things manually for whatever reason, a full reference configuration example can be found in the manual integration test located within this monorepo. Check out the relevant configuration files:

If you are looking for general help in migrating specific rules from TSLint to ESLint, you can check out this incredible project that we depend on in our conversion schematic: https://github.com/typescript-eslint/tslint-to-eslint-config

Premade configs provided by this project

We have several premade configs within this project which you can extend from (and indeed the configs generated by our schematics do just that). For more information about the configs, check out their READMEs

Going fully manual (not recommended)

Our premade configs handle the parser and plugins options for you behind the scenes so that your final config can be more concise.

If for some reason you wanted to not include any of the premade recommended configs, or you wanted to significantly customize your setup, a fully manual example with the right parsers and plugins wired up (but no actual rules activated) would look like this:

{
  "root": true,
  "overrides": [
    {
      "files": ["*.ts"],
      "parser": "@typescript-eslint/parser",
      "parserOptions": {
        "ecmaVersion": 2020,
        "sourceType": "module",
        "project": [
          "tsconfig.app.json",
          "tsconfig.spec.json",
          "e2e/tsconfig.json"
        ],
        "createDefaultProgram": true
      },
      "plugins": ["@typescript-eslint", "@angular-eslint"],
      "rules": {}
    },
    {
      "files": ["*.html"],
      "parser": "@angular-eslint/template-parser",
      "plugins": ["@angular-eslint/template"],
      "rules": {}
    }
  ]
}

Linting HTML files and inline-templates with the VSCode extension for ESLint

If you use vscode-eslint, and want to lint HTML files and inline-templates on your Angular Components, you will need to make sure you add the following to your VSCode settings.json:

// ... more config

"eslint.options": {
  "extensions": [".ts", ".html"]
},

// ... more config

"eslint.validate": [
  "javascript",
  "javascriptreact",
  "typescript",
  "typescriptreact",
  "html"
],

// ... more config

Please see the following issue for more information: microsoft/vscode-eslint#922

Usage without Angular CLI Builder

If you're using this without the Angular CLI Builder don't forget to include .html as one of the file extensions when running the eslint CLI, otherwise templates will not be linted, e.g.:

eslint --ext .ts,.html .

Notes on performance

Background and understanding the trade-offs

As you have hopefully understood from the above section on ESLint configuration what we are dealing with here is a set of tools that were not designed and optimized for this specific use-case.

In software development we are permanently faced with trade-offs. In this case you can think about it this way:

On the one hand...

By using ESLint with Angular (both its TypeScript source code, and its HTML templates), we gain access to a truly massive ecosystem of existing rules, plugins and IDE extensions that we can instantly leverage on our projects.

On the other...

The tooling will never be as fast or memory efficient, or as easy to configure, as something which was purpose built for a narrower use-case and which, well, does less...

TSLint was more in the latter camp - it was purpose built for linting TypeScript source code (note, not HTML), and so it was (depending on the codebase) faster and more efficient at doing it - but it was hugely lacking in community support, features, plugins, rules etc...

Ok, so now we know which side of this particular trade-off we are on. That's an important start.

ESLint configs and performance

Given the increased complexity around configuration, it is possible to end up with non-performant setups if we are not careful.

The first thing is to understand that if you are majorly deviating from the configs that this tooling generates for you automatically, you are greatly increasing the risk of you running into those issues.

The most important piece of ESLint configuration with regards to performance is the parserOptions.project option.

It is what informs typescript-eslint what tsconfigs should be used to create TypeScript Programs behind the scenes as the lint process runs. Without this, it would not be possible to leverage rules which take advantage of type information, we could only lint based on raw syntax.

If parserOptions.project has been configured, by default typescript-eslint will take this as a sign that you only want to lint files that are captured within the scope of the TypeScript Programs which are created. For example, let's say you have a tsconfig.json that contains the following:

{
  // ...more config
  "include" [
    "src/**/*.ts"
  ]
}

If you provide that file as a reference for typescript-eslint, it will conclude that you only want to lint .ts files within src/. If you attempt to lint a file outside of this pattern, it will error. Seems reasonable, right?

Unfortunately, for us in the context of the Angular CLI, we have an added complication. The Angular CLI generates one or more files which are not included in any tsconfig scopes (such as environment.prod.ts).

To prevent this causing errors for users, we therefore enable the createDefaultProgram option for typescript-eslint when we generate your config (it's false by default). This flag tells typescript-eslint not to error in the case in finds a file not in a Program, and instead create a whole new Program to encapsulate that file and then carry on.

This is not ideal, but it works. However, can you see what we've now exposed ourselves to by enabling this?

Now if we run linting - any files which are included in the lint run (e.g. by the glob patterns in the builder config in angular.json) will be linted, and if they are not in scope of an existing tsconfig a whole new Program will be created for each one of them.

Having patterns which do not makes sense together (files to lint vs provided tsconfigs) is usually how seriously non-performant setups can originate from your config. For small projects creating Programs takes a matter of seconds, for large projects, it can take far longer (depending on the circumstances).

Here are some steps you can take if you're linting process feels "unreasonably" slow:

Run the process with debug information from typescript-eslint enabled:

DEBUG=typescript-eslint:* ng lint

Full explanation of this command:
- ng lint is being invoked as normal (you would run the full command above in the same way you run ng lint normally in whatever terminal you use), but we are also setting an environment variable called DEBUG, and giving it a value of typescript-eslint:*.
- DEBUG is a relatively common environment variable because it is supported by some common logging/debugging libraries as a way to toggle how verbose the overall output is at runtime.
- The value of typescript-eslint:* will get picked up by the logger within the typescript-eslint library and cause it to log very verbosely to the standard output of your terminal as it executes.

You will now see a ton of logs which were not visible before. The two most common issues to look out for are:

If you see a lot of logs saying that particular files are not being found in existing Programs (the scenario we described above) and default Programs have to be created
If you see files included for a project that should not be

If you are still having problems after you have done some digging into these, feel free to open and issue to discuss it further, providing as much context as possible (including the logs from the command above).

The ultimate fallback solution to performance problems caused by the Program issues described above is to stop piggybacking on your existing tsconfig files (such as tsconfig.app.json, tsconfig.spec.json etc), and instead create a laser-focused, dedicated tsconfig file for your ESLint use-case:

Create a new tsconfig file at the root of the project within the workspace (e.g. a clear name might be tsconfig.eslint.json)
Set the contents of tsconfig.eslint.json to:
- extend from any root/base tsconfig you may have which sets important compilerOptions
- directly include files you care about for linting purposes

For example, it may look like:

tsconfig.eslint.json

{
  "extends": "./tsconfig.json",
  "include": [
    // adjust "includes" to what makes sense for you and your project
    "src/**/*.ts",
    "e2e/**/*.ts"
  ]
}

Update your project's .eslintrc.json to use the new tsconfig file instead of its existing setting.

For example, the diff might look something like this:

  "parserOptions": {
    "project": [
-     "tsconfig.app.json",
-     "tsconfig.spec.json",
-     "e2e/tsconfig.json"
+     "tsconfig.eslint.json"
    ],
-   "createDefaultProgram": true
+   "createDefaultProgram": false
  },

As you can see, we are also setting "createDefaultProgram" to false because in this scenario we have full control over what files will be included in the Program created behind the scenes for our lint run and we should never need that potentially expensive auto-fallback again. (NOTE: You can also just remove the "createDefaultProgram" setting altogether because its default value is false).

If you are not sure what "createDefaultProgram" does, please reread the section above on ESLint Configs and Performance.

Status of Codelyzer Rules Conversion

The table below shows the status of each Codelyzer Rule in terms of whether or not an equivalent for it has been created within @angular-eslint.

If you see a rule below that has no status against it, then please feel free to open a PR with an appropriate implementation. You can look at the Codelyzer repo and the existing plugins within this repo for inspiration.

Explanation of Statuses
✅ = We have created an ESLint equivalent of this TSLint rule
🚧 = There is an open PR to provide an ESLint equivalent of this TSLint rule
🙅 = This TSLint rule should be replaced by a dedicated code formatter, such as Prettier

Functionality

Codelyzer Rule	ESLint Equivalent	Status
`contextual-decorator`	@angular-eslint/contextual-decorator	✅
`contextual-lifecycle`	@angular-eslint/contextual-lifecycle	✅
`no-attribute-decorator`	@angular-eslint/no-attribute-decorator	✅
`no-lifecycle-call`	@angular-eslint/no-lifecycle-call	✅
`no-output-native`	@angular-eslint/no-output-native	✅
`no-pipe-impure`	@angular-eslint/no-pipe-impure	✅
`prefer-on-push-component-change-detection`	@angular-eslint/prefer-on-push-component-change-detection	✅
`template-accessibility-alt-text`	@angular-eslint/template/accessibility-alt-text	✅
`template-accessibility-elements-content`	@angular-eslint/template/accessibility-elements-content	✅
`template-accessibility-label-for`	@angular-eslint/template/accessibility-label-for	✅
`template-accessibility-tabindex-no-positive`	@angular-eslint/template/no-positive-tabindex	✅
`template-accessibility-table-scope`	@angular-eslint/template/accessibility-table-scope	✅
`template-accessibility-valid-aria`	@angular-eslint/template/accessibility-valid-aria	✅
`template-banana-in-box`	@angular-eslint/template/banana-in-box	✅
`template-click-events-have-key-events`	@angular-eslint/template/click-events-have-key-events	✅
`template-mouse-events-have-key-events`	@angular-eslint/template/mouse-events-have-key-events	✅
`template-no-any`	@angular-eslint/template/no-any	✅
`template-no-autofocus`	@angular-eslint/template/no-autofocus	✅
`template-no-distracting-elements`	@angular-eslint/template/no-distracting-elements	✅
`template-no-negated-async`	@angular-eslint/template/no-negated-async	✅
`use-injectable-provided-in`	@angular-eslint/use-injectable-provided-in	✅
`use-lifecycle-interface`	@angular-eslint/use-lifecycle-interface	✅

Maintainability

Codelyzer Rule	ESLint Equivalent	Status
`component-max-inline-declarations`	@angular-eslint/component-max-inline-declarations	✅
`no-conflicting-lifecycle`	@angular-eslint/no-conflicting-lifecycle	✅
`no-forward-ref`	@angular-eslint/no-forward-ref	✅
`no-input-prefix`	@angular-eslint/no-input-prefix	✅
`no-input-rename`	@angular-eslint/no-input-rename	✅
`no-output-on-prefix`	@angular-eslint/no-output-on-prefix	✅
`no-output-rename`	@angular-eslint/no-output-rename	✅
`no-unused-css`
`prefer-output-readonly`	@angular-eslint/prefer-output-readonly	✅
`relative-url-prefix`	@angular-eslint/relative-url-prefix	✅
`template-conditional-complexity`	@angular-eslint/template/conditional-complexity	✅
`template-cyclomatic-complexity`	@angular-eslint/template/cyclomatic-complexity	✅
`template-i18n`	@angular-eslint/template/i18n	✅
`template-no-call-expression`	@angular-eslint/template/no-call-expression	✅
`template-use-track-by-function`	@angular-eslint/template/use-track-by-function	✅
`use-component-selector`	@angular-eslint/use-component-selector	✅
`use-component-view-encapsulation`	@angular-eslint/use-component-view-encapsulation	✅
`use-pipe-decorator`	@angular-eslint/use-pipe-decorator	✅
`use-pipe-transform-interface`	@angular-eslint/use-pipe-transform-interface	✅

Style

Codelyzer Rule	ESLint Equivalent	Status
`angular-whitespace`	N/A, see explanation above	🙅
`component-class-suffix`	@angular-eslint/component-class-suffix	✅
`component-selector`	@angular-eslint/component-selector	✅
`directive-class-suffix`	@angular-eslint/directive-class-suffix	✅
`directive-selector`	@angular-eslint/directive-selector	✅
`import-destructuring-spacing`	N/A, see explanation above	🙅
`no-host-metadata-property`	@angular-eslint/no-host-metadata-property	✅
`no-inputs-metadata-property`	@angular-eslint/no-inputs-metadata-property	✅
`no-outputs-metadata-property`	@angular-eslint/no-outputs-metadata-property	✅
`no-queries-metadata-property`	@angular-eslint/no-queries-metadata-property	✅
`pipe-prefix`	@angular-eslint/pipe-prefix	✅
`prefer-inline-decorator`	N/A, see explanation above	🙅

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