Typescript lint rules This rule reports when an as assertion is doing the same job as a ! These rules care about how the code looks rather than how it executes: unicode-bom. "Typed linting", or enabling ESLint rules to tap into the power of the TypeScript type checker, is one of the best parts of typescript-eslint. Method chaining is a common pattern in OOP languages and TypeScript provides a special polymorphic this type to facilitate it. Duplicate values make the code overly verbose and generally reduce readability. json receives the configuration for the typescript compiler like allowing javascript files, the location of your files, etc. @ts-ignore directive comments instruct the TypeScript compiler to ignore the type errors on the next line. You can then test your rule by providing the type-aware config: There is actually a way to have the catch() and then() callback variables use the unknown type without an explicit type annotation at the call sites, but it has the drawback that it involves overriding global type declarations. MIT license Security policy. It allows creating a series of assertions called lint rules around what your code should look or behave like, as well as auto-fixer suggestions to improve your code for you, and You can tell ESLint to lint your code using the following command: eslint --ext . As of v7 and ESLint 9, most users should be using the typescript-eslint package. allowDefaultProject: ["*. eslintrc. cts, . This rule extends the base eslint/default-param-last rule. However, developers typically expect each constituent to be unique within its intersection or union. [1] - TypeScript computes type information lazily, so us asking for the errors it would produce from the compiler would take an additional ~100ms per file. If you're compiling your TypeScript code to a different folder, make sure to use that instead of dist. Automate Linting: Incorporate linting into your build process or TypeScript linting is the process of analyzing TypeScript code to detect potential errors, enforce coding standards, and improve code quality. js for Try this rule in the playground ↗. These rules have been deprecated in accordance with TypeScript Lint Rules and ASTs Interested in how these ASTs work with ESLint rules? We collaborated with our friends at Sourcegraph on a Tour de Source on typescript-eslint. These rules find errors related to TypeScript features: adjacent-overload-signatures - Enforces function TypeScript lint rules provide guidelines and constraints to ensure consistent and error-free code across a project. js will run ESLint for all files in the pages/, app/, components/, lib/, and src/ directories. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling String#match is defined to work the same as RegExp#exec when the regular expression does not include the g flag. It gets even more powerful, however, when TypeScript type-checker is layered on top of it when analyzing TypeScript files, which is something that @typescript-eslint allows us to do. TSLint is an extensible static analysis tool that checks TypeScript code for readability, maintainability, and functionality errors. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. ☘️ What is TypeScript ESLint? Customize Rules: Tailor ESLint rules to fit your project's specific requirements by modifying the configuration file. It is widely supported across modern editors & build systems and can be customized with your own lint rules, configurations, and formatters. Now, let us first write the rule in TypeScript: import * as Lint from " tslint "; import * as ts from " typescript "; Given a walker, TypeScript’s parser visits the AST using the visitor pattern. Read on to learn how ESLint rules use ASTs to analyze code files and, thanks to @typescript-eslint/parser, call TypeScript's type checking APIs to analyze code. The void operator is a useful tool to convey the programmer's intent to discard a value. <script> content of . If the type is known, describing it in an interface or type Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. The modifiers exist solely in the type system and just serve to describe who is allowed to access those members. Rules get added as keys of this rules attribute, and you can normally find the eslint base rules here ESLint is powerful linter by itself, able to work on the syntax of your source files and assert things about based on the rules you configure. * @returns a probably unique name. Resources . tslint. For TypeScript projects, integrating ESLint is a game-changer Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. Resources tsconfig. ts, . Readme License. We also provide a plethora of powerful rules that utilize the power of TypeScript's type information. Note: using the build artifacts with npm link does not work correctly, since there will be a mismatch between the typescript version used by the consumer code and the typescript version used by the lint rules code. Calling an any-typed value as a function creates a potential type safety hole and . In this blog post, we'll give a high-level overview of how linting with type information works, why ESLint statically analyzes your code to quickly find problems. ts and . Resources Type-Aware Testing . It adds support for optional parameters. This means that TypeScript doesn't have to try to infer the type, and avoids the common pitfalls that come with assertions. Rules. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling type checked rules. Packages 0. Custom properties. ts*"] to enable type checking on all test files. This rule has been moved to the ESLint stylistic plugin. 13. */ export ESLint will lint all TypeScript compatible files within the current folder, and will output the results to your terminal. Installation Run oxlint directly at the root of your repository: Instead, our tooling exists to augment TypeScript's built in checks with lint rules that consume the type information in new ways beyond just verifying the runtime correctness of your code. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling TSLint removes rules when they are added to TypeScript proper. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling Typescript style guide, linter, and formatter using StandardJS - standard/ts-standard If you want to discuss the rules, please visit the rules configuration repo eslint-config-standard-with-typescript. TypeScript enums are allowed to assign numeric or string values to their members. js,. This proved to be a little problematic when I tried to create the configuration file for ESLint. When writing TypeScript libraries that could be used by JavaScript users, however, it's typically safer to expose these literals using getters, since the readonly modifier is enforced at compile type. Resources Rule source; Test source; Taken with ️ from ESLint core. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling By default any type you assign can take the values undefined and null along with any type declarations you have made. See configs/stylistic-type-checked. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling Note that stylistic-type-checked does not replace recommended-type-checked or strict-type-checked. 12 watching Forks. Even then it doesn't detect unused exported variables because each file is Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. tsx) with the rules defined in eslint-config-xo-typescript#use-with-xo. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling Some TypeScript applications store literal values on classes using fields with the readonly modifier to prevent them from being reassigned. 50 stars Watchers. In this case, Lint rules encode logic for syntactic & semantic checks of TypeScript source code. Most rule tests specify parserOptions. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling TypeScript supports types ("constituents") within union and intersection types being duplicates of each other. { "compilerOptions": { "strictNullChecks": true } } Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. This rule reports when a type assertion does not change the type of an expression. Examples Linting custom directories and files. ts. Deprecated. To test the package in a project, run On the ESLint page of the documentation there is a section named TypeScript. json is the configuration for TSLint, TSLint helps you to detect bad coding practices or follow a coding style, you can configure its options like disallow unused variables, no logging to the console, etc. The @typescript-eslint/* packages are all stored in our GitHub monorepo. Languages. lint rule fixers can conflict (apply to the same code range), forcing the linter to perform an additional cycle to attempt to apply a fixer to a clean set of code. See Custom Rules for the updated documentation on creating custom rules with typescript-eslint. In . See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. It will suggest instead pass the asserted type to Array#reduce as a generic type argument. vue, . But enabling the type checker in repositories with multiple tsconfig. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after any two lint rules can't share config, meaning one lint rule's fixer might introduce a violation of another lint rule's fixer (eg one lint rule might use the incorrect indentation character). See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling JavaScript and TypeScript by their extensions js, mjs, cjs, jsx, ts, mts, cts and tsx. This rule reports on explicit uses of the any keyword as a type annotation. This rule reports when a String#match call can be replaced with an equivalent RegExp#exec. Then add the things we want to ignore. stylistic rules. ts files where I can use the typescript lint rules. Require or disallow Unicode byte order mark (BOM) Categories: Extends. Other Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. 15 forks Report repository Releases 4 tags. For example, the library better-TypeScript-lib sets this up globally for your project (see the relevant lines in the better-TypeScript-lib source code for Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. TSLint already has a fairly straightforward API for adding custom lint rules, but writing the actual logic of the rules can be quite tricky! We can make that a lot easier by using powerful AST node I had the same issue in JS, and the problem was that I was using pluginJs. TypeScript allows placing explicit public, protected, and private accessibility modifiers in front of class members. Improve this answer. XO will handle the @typescript-eslint/parser project option automatically even if you don't have a However, because TypeScript utilizes internal caching, a project's first type-aware lint rule will almost always seem the slowest. IDE To get the most benefit from eslint, it is recommended to configure it with your IDE. projectService. tsconfig (see the previous guide). See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling Linting is an essential part of modern software development, ensuring that code adheres to predefined standards and best practices. Preferable alternatives to any include:. By enforcing these rules, developers can identify potential In this guide, we’ll walk you through setting up TypeScript ESLint from scratch and configuring it to improve your development workflow. d. Security policy Activity. No packages published . Rule source Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. Even then it doesn't detect unused exported variables because each file is analysed individually. Typed linting rules as provided by typescript-eslint are the most powerful JavaScript/TypeScript linting in common use today. This utility was designed to be the npm run lint:standard checks for code errors and format according to standard; npm test Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. This rule looks for calls to Array#reduce, and reports if an initial value is being passed & asserted. Leaving as assertions in the codebase increases visual clutter and harms code readability, so it's generally best practice to remove them if they don't change the type of an expression. : "@typescript-eslint/indent": "off" This will deactivate the @typescript-eslint/indent rule for your project. So the custom rule was overwritten by the recommended rules ( in the eslint. ts for the exact contents of this config. Despite your best intentions, the any type can sometimes leak into your codebase. mts, . In your TypeScript config file (tsconfig. It says that when creating a new project set up to use TypeScript, it should add TypeScript-specific lint rules and the content of the . By default, Next. json files can be annoying to set up. Type checked lint rules are more powerful than As an aside, make sure you are using the Typescript version of no-unused-vars rule. typescript-eslint . Mixing enum member types is generally considered confusing and a bad practice. configs. The monorepo is built and released with Nx. When investigating which lint rules are the slowest in your project, be sure to run them one at a time and compare those timing measurements separately. astro and . See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after However, because TypeScript utilizes internal caching, a project's first type-aware lint rule will almost always seem the slowest. Linters help developers catch There are three modes for a rule in eslint: off, warn, and error. json) you can set the StrictNullChecks compiler option to true. The ext flag is used to specify which file extensions ESLint should consider when searching for files in the target directory. Quick void in TypeScript refers to a function return that is meant to be ignored. In my configuration file. Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. stylistic-type-checked adds additional rules. My config file looks something like below (The rules section is just representational). We hope these wrapper APIs make it more convenient to write lint rules that rely on the awesome power of TypeScript's type checking. 🔧 Fix. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling The exported class must always be named Rule and extend from Lint. Accessing a member of an any-typed value creates a potential type safety hole and Now run npm i && npx ts-jest config:init && npm run test. Follow Typescript lint marking errors. AbstractRule. So the rule walkers only need to override the appropriate Common TypeScript lint rules/preferences for Ionic. Keeping to consistently using one of the two can help improve code readability. When Not To Use It . config. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling XO will automatically lint TypeScript files (. json file should look like this: Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. recommended AFTER my custom rules. I had the main set of rules for the JS files and then created an override section for *. 💡 Suggestions. Visit the next page for a typed rules setup guide. Share. Using any disables many type checking rules and is generally best used only as a last resort or when prototyping code. . * * @param baseName a suggested name to make unique. Editor’s note: This article was last updated by Muhammed Ali on 12 September 2024 to include updates on compiling TypeScript, setting up ESLint, and integrating Prettier for consistent formatting. Class methods that explicitly declare a return type of the class name instead of this make it harder for extending classes to call that method: the returned object will be typed as the base class, not the derived class. Contributors 13. No support for: type-aware rules defined by typescript-eslint. Type checked lint rules are more powerful than traditional lint rules That way after merging your commit, all they have to do is yarn lint:build-rules and npm install. Even worse, specifying the wrong include paths could result in incorrect rule reports and/or unexpectedly slow lint times. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling Depending on which one of these two rules you want you can just simply deactivate the other one by adding this to you rules eg. So, it compiles and tests run fine, all is good? Nope! Let’s remove the @ts-ignore directive comments and see what TypeScript can be told an expression is a different type than expected using as type assertions. Type-aware rules can be tested in almost exactly the same way as regular code, using parserOptions. We recommend using an appropriate integration to view warnings and errors directly in your code editor during development. As developers, we usually start a project by adding configurations and scripts for linting, then formatting and type checking for our codebase syntax and style. See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling Options . There's still a lot of rules in there that TypeScript doesn't check for, though, so if you care about it, you'll probably want to use both. eslintrc, add a new attribute to the json object called "rules". Stars. Resources. In the following code sample, we're ignoring the dist/ folder that contains the compiled TypeScript code. Follow There are two common ways to assert to TypeScript that a value is its type without null or undefined:: Non-null assertion; as: Traditional type assertion with a coincidentally equivalent type! non-null assertions are generally preferred for requiring less code and being harder to fall out of sync as types change. We can see that the TSX compiles fine due to the // @ts-ignore directive comments. You should be able to find this in your . This rule is not configurable. This rule reports when a class method Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. 🧙 Why. In the future, we may add more wrapper APIs, and may even add internal caching to those APIs to improve performance. svelte files. However, you can specify which directories using the dirs option in the eslint config in next. It exports configurations for ESLint and brings along the corresponding versions of other packages as dependencies. The any type in TypeScript is a dangerous "escape hatch" from the type system. RegExp#exec may also be slightly faster than String#match; this is the reason to choose it as typescript-eslint is now your best option for linting TypeScript. Take the following Typescript arrow function: /** * Returns a probably unique component name. Packages. mjs ). Most enums contain either all numbers or all strings, but in theory you can mix-and-match within the same enum. ofdcxe vpmedek btgp awzw pror dqme sxtir lnfwe wrzxykl gjvkc