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Linting TypeScript

Last modified: 20 October 2022

Required plugin:

Javascript and TypeScript -  The plugin is bundled with AppCode and enabled by default.

The recommended linter for TypeScript code is ESLint which brings a wide range of linting rules that can also be extended with plugins. AppCode shows warnings and errors reported by ESLint right in the editor, as you type. Learn more from ESLint.

note

You can also use TSLint as described below. Note that TSLint has been deprecated as of 2019, see the TSLint official website for details.

AppCode highlights errors reported by ESLint in .ts and .tsx files when @typescript-eslint/parser is set as a parser in your project ESLint configuration. Learn more from the readme file in the typescript-eslint repo.

Install and configure ESLint

  1. In the embedded Terminal (Alt+F12) , type one of the following commands:

    • npm install --g eslint for global installation.

    • npm install --save-dev eslint to install ESLint as a development dependency.

  2. By default, ESLint is disabled. Enable it on the Preferences | Languages and Frameworks | JavaScript | Code Quality Tools | ESLint as described in Activate and configure ESLint in AppCode".

Use ESLint for TypeScript in a new project

  1. In the embedded Terminal (Alt+F12) , type:

    npm install @typescript-eslint/parser @typescript-eslint/eslint-plugin --save-dev

    note

    If you installed ESLint globally, install @typescript-eslint/eslint-plugin globally as well. Learn more about installation and versions compatibility from the @typescript-eslint/eslint-plugin official documentation.

  2. In the .eslintrc configuration file or under eslintConfig in package.json, add:

    {
    "parser": "@typescript-eslint/parser",
    "plugins": [
        "@typescript-eslint"
    ],
    "extends": [
        "plugin:@typescript-eslint/recommended"
    ]
}

Suppress linting TypeScript code with ESLint

  • If you are already using @typescript-eslint/parser but you do not want to check TypeScript code with ESLint, add .ts or .tsx to the .eslintignore file.

ESLint 4.0

If you are using previous versions of ESLint, you have to install babel-eslint, typescript-eslint-parser, or eslint-plugin-typescript because ESLint 4.0 and earlier do not support scoped packages.

Use babel-eslint

  1. In the embedded Terminal (Alt+F12) , type:

    npm install eslint babel-eslint --save-dev

    Learn more about installation and versions compatibility from the babel-eslint official documentation.

  2. In the .eslintrc configuration file or under eslintConfig in package.json, add:

    {
    "parser": "babel-eslint"
}

Use typescript-eslint-parser

  1. In the embedded Terminal (Alt+F12) , type:

    npm install typescript-eslint-parser --save-dev

    Learn more from the typescript-eslint-parser official documentation.

  2. In the .eslintrc configuration file or under eslintConfig in package.json, add:

    {
    "parser": "typescript-eslint-parser"
}

Use eslint-plugin-typescript

  1. In the embedded Terminal (Alt+F12) , type:

    npm install typescript-eslint-parser eslint-plugin-typescript --save-dev

    note

    If you installed ESLint globally, install eslint-plugin-typescript globally as well. Learn more from the eslint-plugin-typescript official documentation.

  2. In the .eslintrc configuration file or under eslintConfig in package.json, add:

    {
    "parser": "typescript-eslint-parser",
    "plugins": [
        "eslint-plugin-typescript"
    ]
}

TSLint

You can also use the TSLint code verification tool from inside AppCode and check your TypeScript code for most common mistakes without running the application. When the tool is activated, it lints all the opened TypeScript files and marks the detected problems.

warning

TSLint has been deprecated as of 2019, see the TSLint official website for details.

It is recommended that you check your TypeScript code using ESLint as described above.

To view the description of a problem, hover over the highlighted code. By default, AppCode marks detected problems based on the severity levels from the TSLint configuration file. See Configuring TSLint highlighting to learn how to override these settings.

TSLint: errors and warnings are highlighted, the description of a problem is shown in a tooltip.

Before you start

Installing TSLint

Activating and configuring TSLint in AppCode

By default, AppCode uses the TSLint package from the project node_modules folder and the tslint.json configuration file from the folder where the current file is stored. If no tslint.json is found in the current file folder, AppCode will look for one in its parent folders up to the project root.

If you have several package.json files with TSLint listed as a dependency, AppCode starts a separate process for each package.json and processes everything below it. This lets you apply a specific TSLint version or a specific set of plugins to each path in a monorepo or a project with multiple TSLint configurations.

This behavior is default in all new AppCode projects. To enable it in a previously created project, go to Languages & Frameworks | TypeScript | TSLint in the Preferences dialog (Ctrl+Alt+S) and select the Automatic TSLint configuration option.

You can also configure TSLint manually to use a custom TSLint package and tslint.json and specify some additional rules.

Configuring highlighting for TSLint

By default, AppCode marks the detected errors and warnings based on the severity levels from the TSLint configuration file. For example, errors are highlighted with a red squiggly line, while warnings are marked with a yellow background. See Code inspections and Change inspection severity for details.

Change the severity level of a rule in the TSLint configuration

  • In TSLint configuration file, locate the rule you want to edit and set its ID to warning or to error. Learn more from the TSLint official website.

You can override the severities from the TSLint configuration file so that AppCode ignores them and shows everything reported by the linter as errors, warnings, or in a custom color.

Ignore the severity levels from the configuration

  1. In the Preferences dialog (Ctrl+Alt+S), go to Editor | Inspections. The Inspections page opens.

  2. In the central pane, go to TypeScript | TSLint.

  3. In the right-hand pane, clear the Use rule severity from the configuration file checkbox and select the severity level to use instead of the default one.

    Specifying a custom severity level for TSLint

Importing code style from a TSLint configuration file

AppCode understands some TSLint rules that are described in tslint.json, tslint .yaml, or tslint.yml configuration files and lets you apply them to the TypeScript code style configuration in your project.

  • When you open your project for the first time, AppCode imports the code style from the project tslint.json, tslint.yaml, or tslint.yml automatically.

  • If tslint.json, tslint.yaml, or tslint.yml is updated (manually or from your version control), open it in the editor and choose Apply TSLint Code Style Rules from the context menu.

    Import TSLint code style rules from the editor: context menu

    Alternatively, just answer Yes to the "Apply code style from TSLint?" question on top of the file.

    AppCode suggests importing the code style from tslint.json

TSLint quick-fixes

AppCode lets you automatically fix some of the issues that TSLint reports.

You can suppress TSLint rules for the current file and even for the current line. AppCode automatically generates disable comments in the format /* tslint:disable:<rule name> or // tslint:disable-next-line:<rule name> and places them on top of the file or above the current line respectively.

Suppress a TSLint rule on the fly

  1. Position the caret at an error or a warning reported by TSLint and press Alt+Enter.

  2. Select the quick-fix for the rule that you want to disable and press Right.

  3. From the list, select Suppress <rule name> for current file or Suppress <rule name> for current line.

    Disabling TSLint rules on the fly by adding disable comments

See also

Procedures

External Links