tslint

What is tslint?

The tslint npm package is a static analysis tool that checks TypeScript code for readability, maintainability, and functionality errors. It is widely used to enforce a consistent code style by checking the code against a set of linting rules.

What are tslint's main functionalities?

Linting TypeScript Files

This feature allows you to lint TypeScript files by specifying a configuration file and a pattern to match files. The command will process all TypeScript files in the 'src' directory and its subdirectories.

tslint -c tslint.json 'src/**/*.ts'

Fixing Linting Errors Automatically

This feature automatically fixes linting errors that can be corrected without human intervention. It is useful for fixing simple issues like whitespace or semicolon usage.

tslint --fix -c tslint.json 'src/**/*.ts'

Custom Rules

This feature allows you to use custom linting rules in addition to the predefined rules. You can specify a directory containing custom rule definitions to be applied to your code.

tslint -c tslint.json 'src/**/*.ts' --rules-dir custom_rules

Other packages similar to tslint

eslint

ESLint is a popular linting tool for JavaScript and TypeScript. It is highly configurable and extendable, with a large ecosystem of plugins. ESLint has effectively replaced TSLint as the preferred linter for TypeScript after TSLint's deprecation.

prettier

Prettier is an opinionated code formatter that supports many languages, including TypeScript. While it does not perform static code analysis, it formats code to a consistent style. Prettier can be used alongside linters like ESLint.

stylelint

Stylelint is a modern linter that helps you avoid errors and enforce conventions in your stylesheets. Although it is primarily used for CSS, it can be used in conjunction with PostCSS to lint SCSS, Sass, Less, and other CSS-like languages.

README

TSLint

An extensible linter for the TypeScript language.

TSLint supports:

• custom lint rules
• custom formatters (failure reporters)
• inline disabling / enabling of rules
• configuration presets (tslint:latest, tslint-react, etc.) & composition
• integration with msbuild, grunt, gulp, atom, eclipse, emacs, sublime, vim, visual studio, vscode, webstorm, and more

Table of Contents

• Installation
• Usage
• Core Rules
• Rule Flags
• Custom Rules
• Development
• Creating a new release

Installation

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CLI

npm install -g tslint typescript

Library

npm install tslint typescript

Peer dependencies

typescript is a peer dependency of tslint. This allows you to update the compiler independently from the linter. This also means that tslint will have to use the same version of tsc used to actually compile your sources.

Breaking changes in the latest dev release of typescript@next might break something in the linter if we haven't built against that release yet. If this happens to you, you can try:

1. picking up tslint@next, which may have some bugfixes not released in tslint@latest (see release notes here).
2. rolling back typescript to a known working version.

Usage

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Please ensure that the TypeScript source files compile correctly before running the linter.

Configuration

TSLint is configured via a file named tslint.json. This file is loaded from the current path, or the user's home directory, in that order.

The configuration file specifies which rules are enabled and their options. These configurations may extend other ones via the "extends" field in tslint.json.

{
  /*
   * Possible values:
   * - the name of a built-in config
   * - the name of an NPM module which has a "main" file that exports a config object
   * - a relative path to a JSON file
   */
  "extends": "tslint:latest",
  "rules": {
    /*
     * Any rules specified here will override those from the base config we are extending
     */
    "no-constructor-vars": true
  },
  "rulesDirectory": [
    /*
     * A list of relative or absolute paths to directories that contain custom rules.
     * See the Custom Rules documentation below for more details.
     */
  ]
}

Built-in configs include tslint:latest and tslint:recommended. You may inspect their source here.

tslint:recommended is a stable, somewhat opinionated set of rules which we encourage for general TypeScript programming. This configuration follows semver, so it will not have breaking changes across minor or patch releases.

tslint:latest extends tslint:recommended and is continuously updated to include configuration for the latest rules in every TSLint release. Using this config may introduce breaking changes across minor releases as new rules are enabled which cause lint failures in your code. When TSLint reaches a major version bump, tslint:recommended will be updated to be identical to tslint:latest.

See the core rules list below for descriptions of all the rules.

CLI

usage: tslint [options] file ...

Options:

-c, --config          configuration file
--force               return status code 0 even if there are lint errors
-h, --help            display detailed help
-i, --init            generate a tslint.json config file in the current working directory
-o, --out             output file
-r, --rules-dir       rules directory
-s, --formatters-dir  formatters directory
-e, --exclude         exclude globs from path expansion
-t, --format          output format (prose, json, verbose, pmd, msbuild, checkstyle)  [default: "prose"]
--test                test that tslint produces the correct output for the specified directory
--project             path to tsconfig.json file
--type-check          enable type checking when linting a project
-v, --version         current version

tslint accepts the following command-line options:

-c, --config:
    The location of the configuration file that tslint will use to
    determine which rules are activated and what options to provide
    to the rules. If no option is specified, the config file named
    tslint.json is used, so long as it exists in the path.
    The format of the file is { rules: { /* rules list */ } },
    where /* rules list */ is a key: value comma-separated list of
    rulename: rule-options pairs. Rule-options can be either a
    boolean true/false value denoting whether the rule is used or not,
    or a list [boolean, ...] where the boolean provides the same role
    as in the non-list case, and the rest of the list are options passed
    to the rule that will determine what it checks for (such as number
    of characters for the max-line-length rule, or what functions to ban
    for the ban rule).

-e, --exclude:
    A filename or glob which indicates files to exclude from linting.
    This option can be supplied multiple times if you need multiple
    globs to indicate which files to exclude.

--force:
    Return status code 0 even if there are any lint errors.
    Useful while running as npm script.

-i, --init:
    Generates a tslint.json config file in the current working directory.

-o, --out:
    A filename to output the results to. By default, tslint outputs to
    stdout, which is usually the console where you're running it from.

-r, --rules-dir:
    An additional rules directory, for user-created rules.
    tslint will always check its default rules directory, in
    node_modules/tslint/lib/rules, before checking the user-provided
    rules directory, so rules in the user-provided rules directory
    with the same name as the base rules will not be loaded.

-s, --formatters-dir:
    An additional formatters directory, for user-created formatters.
    Formatters are files that will format the tslint output, before
    writing it to stdout or the file passed in --out. The default
    directory, node_modules/tslint/build/formatters, will always be
    checked first, so user-created formatters with the same names
    as the base formatters will not be loaded.

-t, --format:
    The formatter to use to format the results of the linter before
    outputting it to stdout or the file passed in --out. The core
    formatters are prose (human readable), json (machine readable)
    and verbose. prose is the default if this option is not used.
    Other built-in options include pmd, msbuild, checkstyle, and vso.
    Additional formatters can be added and used if the --formatters-dir
    option is set.

--test:
    Runs tslint on the specified directory and checks if tslint's output matches
    the expected output in .lint files. Automatically loads the tslint.json file in the
    specified directory as the configuration file for the tests. See the
    full tslint documentation for more details on how this can be used to test custom rules.

--project:
    The location of a tsconfig.json file that will be used to determine which
    files will be linted.

--type-check
    Enables the type checker when running linting rules. --project must be
    specified in order to enable type checking.

-v, --version:
    The current version of tslint.

-h, --help:
    Prints this help message.

Library

const Linter = require("tslint");
const fs = require("fs");

const fileName = "Specify file name";
const configuration = {
    rules: {
        "variable-name": true,
        "quotemark": [true, "double"]
    }
};
const options = {
    formatter: "json",
    configuration: configuration,
    rulesDirectory: "customRules/",
    formattersDirectory: "customFormatters/"
};

const fileContents = fs.readFileSync(fileName, "utf8");
const linter = new Linter(fileName, fileContents, options);
const result = linter.lint();

Type Checking

To enable rules that work with the type checker, a TypeScript program object must be passed to the linter when using the programmatic API. Helper functions are provided to create a program from a tsconfig.json file. A project directory can be specified if project files do not lie in the same directory as the tsconfig.json file.

const program = Linter.createProgram("tsconfig.json", "projectDir/");
const files = Linter.getFileNames(program);
const results = files.map(file => {
    const fileContents = program.getSourceFile(file).getFullText();
    const linter = new Linter(file, fileContents, options, program);
    return result.lint();
});

When using the CLI, the --project flag will automatically create a program from the specified tsconfig.json file. Adding --type-check then enables rules that require the type checker.

Core Rules

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[See the TSLint website for a list of core rules included in the tslint package.] (http://palantir.github.io/tslint/rules/)

Core Formatters

Formatters are used to format the results of the linter before outputting it to stdout or the configured output file. The core formatters are:

• prose: human readable (default)
• json: machine readable
• verbose: human readable (includes rule names)
• pmd
• msbuild
• checkstyle
• vso

Rule Flags

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You may enable/disable TSLint or a subset of rules within certain lines of a file with the following comment rule flags:

• /* tslint:disable */ - Disable all rules for the rest of the file
• /* tslint:enable */ - Enable all rules for the rest of the file
• /* tslint:disable:rule1 rule2 rule3... */ - Disable the listed rules for the rest of the file
• /* tslint:enable:rule1 rule2 rule3... */ - Enable the listed rules for the rest of the file
• // tslint:disable-next-line - Disables all rules for the following line
• someCode(); // tslint:disable-line - Disables all rules for the current line
• // tslint:disable-next-line:rule1 rule2 rule3... - Disables the listed rules for the next line
• etc.

Rules flags enable or disable rules as they are parsed. Disabling an already disabled rule or enabling an already enabled rule has no effect.

For example, imagine the directive /* tslint:disable */ on the first line of a file, /* tslint:enable:ban class-name */ on the 10th line and /* tslint:enable */ on the 20th. No rules will be checked between the 1st and 10th lines, only the ban and class-name rules will be checked between the 10th and 20th, and all rules will be checked for the remainder of the file.

Custom Rules

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Custom rule sets from Palantir

• tslint-react - Lint rules related to React & JSX.

Custom rule sets from the community

If we don't have all the rules you're looking for, you can either write your own custom rules or use custom rules that others have developed. The repos below are a good source of custom rules:

• ESLint rules for TSLint - Improve your TSLint with the missing ESLint Rules
• tslint-microsoft-contrib - A set of TSLint rules used on some Microsoft projects
• codelyzer - A set of tslint rules for static code analysis of Angular 2 TypeScript projects
• vrsource-tslint-rules

Writing custom rules

TSLint ships with a set of core rules that can be configured. However, users are also allowed to write their own rules, which allows them to enforce specific behavior not covered by the core of TSLint. TSLint's internal rules are itself written to be pluggable, so adding a new rule is as simple as creating a new rule file named by convention. New rules can be written in either TypeScript or JavaScript; if written in TypeScript, the code must be compiled to JavaScript before invoking TSLint.

Rule names are always camel-cased and must contain the suffix Rule. Let us take the example of how to write a new rule to forbid all import statements (you know, for science). Let us name the rule file noImportsRule.ts. Rules can be referenced in tslint.json in their kebab-case forms, so "no-imports": true would turn on the rule.

Now, let us first write the rule in TypeScript. A few things to note:

• We import tslint/lib/lint to get the whole Lint namespace instead of just the Linter class.
• The exported class must always be named Rule and extend from Lint.Rules.AbstractRule.

import * as ts from "typescript";
import * as Lint from "tslint/lib/lint";

export class Rule extends Lint.Rules.AbstractRule {
    public static FAILURE_STRING = "import statement forbidden";

    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
        return this.applyWithWalker(new NoImportsWalker(sourceFile, this.getOptions()));
    }
}

// The walker takes care of all the work.
class NoImportsWalker extends Lint.RuleWalker {
    public visitImportDeclaration(node: ts.ImportDeclaration) {
        // create a failure at the current position
        this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING));

        // call the base version of this visitor to actually parse this node
        super.visitImportDeclaration(node);
    }
}

Given a walker, TypeScript's parser visits the AST using the visitor pattern. So the rule walkers only need to override the appropriate visitor methods to enforce its checks. For reference, the base walker can be found in syntaxWalker.ts.

We still need to hook up this new rule to TSLint. First make sure to compile noImportsRule.ts:

tsc -m commonjs --noImplicitAny noImportsRule.ts node_modules/tslint/lib/tslint.d.ts

Then, if using the CLI, provide the directory that contains this rule as an option to --rules-dir. If using TSLint as a library or via grunt-tslint, the options hash must contain "rulesDirectory": "...". If you run the linter, you'll see that we have now successfully banned all import statements via TSLint!

Final notes:

• Core rules cannot be overwritten with a custom implementation.
• Custom rules can also take in options just like core rules (retrieved via this.getOptions()).

Custom Formatters

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Just like rules, additional formatters can also be supplied to TSLint via --formatters-dir on the CLI or formattersDirectory option on the library or grunt-tslint. Writing a new formatter is simpler than writing a new rule, as shown in the JSON formatter's code.

import * as ts from "typescript";
import * as Lint from "tslint/lib/lint";

export class Formatter extends Lint.Formatters.AbstractFormatter {
    public format(failures: Lint.RuleFailure[]): string {
        var failuresJSON = failures.map((failure: Lint.RuleFailure) => failure.toJson());
        return JSON.stringify(failuresJSON);
    }
}

Such custom formatters can also be written in JavaScript. Formatter files are always named with the suffix Formatter and the exported class within the file must be named Formatter. A formatter is referenced from TSLint without its suffix.

Development

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Quick Start

git clone [e-mail]:palantir/tslint.git
npm install
grunt

next branch

The next branch of this repo tracks the latest TypeScript compiler nightly release as a peerDependency. This allows you to develop the linter and its rules against the latest features of the language. Releases from this branch are published to npm with the next dist-tag, so you may install the latest dev version of TSLint via npm install tslint@next.

Creating a new release

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1. Bump the version number in package.json and src/tslint.ts
2. Add release notes in CHANGELOG.md
3. Run grunt to build the latest sources
4. Commit with message Prepare release <version>
5. Run npm publish
6. Create a git tag for the new release and push it (see existing tags here)