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‎.cursor/rules/ultracite.mdc‎

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---
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description: Ultracite Rules - AI-Ready Formatter and Linter
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globs: "**/*.{ts,tsx,js,jsx}"
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alwaysApply: true
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---
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# Project Context
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Ultracite enforces strict type safety, accessibility standards, and consistent code quality for JavaScript/TypeScript projects using Biome's lightning-fast formatter and linter.
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## Key Principles
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- Zero configuration required
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- Subsecond performance
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- Maximum type safety
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- AI-friendly code generation
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## Before Writing Code
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1. Analyze existing patterns in the codebase
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2. Consider edge cases and error scenarios
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3. Follow the rules below strictly
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4. Validate accessibility requirements
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## Rules
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### Accessibility (a11y)
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- Don't use `accessKey` attribute on any HTML element.
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- Don't set `aria-hidden="true"` on focusable elements.
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- Don't add ARIA roles, states, and properties to elements that don't support them.
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- Don't use distracting elements like `<marquee>` or `<blink>`.
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- Only use the `scope` prop on `<th>` elements.
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- Don't assign non-interactive ARIA roles to interactive HTML elements.
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- Make sure label elements have text content and are associated with an input.
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- Don't assign interactive ARIA roles to non-interactive HTML elements.
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- Don't assign `tabIndex` to non-interactive HTML elements.
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- Don't use positive integers for `tabIndex` property.
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- Don't include "image", "picture", or "photo" in img alt prop.
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- Don't use explicit role property that's the same as the implicit/default role.
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- Make static elements with click handlers use a valid role attribute.
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- Always include a `title` element for SVG elements.
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- Give all elements requiring alt text meaningful information for screen readers.
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- Make sure anchors have content that's accessible to screen readers.
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- Assign `tabIndex` to non-interactive HTML elements with `aria-activedescendant`.
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- Include all required ARIA attributes for elements with ARIA roles.
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- Make sure ARIA properties are valid for the element's supported roles.
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- Always include a `type` attribute for button elements.
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- Make elements with interactive roles and handlers focusable.
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- Give heading elements content that's accessible to screen readers (not hidden with `aria-hidden`).
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- Always include a `lang` attribute on the html element.
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- Always include a `title` attribute for iframe elements.
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- Accompany `onClick` with at least one of: `onKeyUp`, `onKeyDown`, or `onKeyPress`.
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- Accompany `onMouseOver`/`onMouseOut` with `onFocus`/`onBlur`.
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- Include caption tracks for audio and video elements.
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- Use semantic elements instead of role attributes in JSX.
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- Make sure all anchors are valid and navigable.
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- Ensure all ARIA properties (`aria-*`) are valid.
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- Use valid, non-abstract ARIA roles for elements with ARIA roles.
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- Use valid ARIA state and property values.
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- Use valid values for the `autocomplete` attribute on input elements.
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- Use correct ISO language/country codes for the `lang` attribute.
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### Code Complexity and Quality
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- Don't use consecutive spaces in regular expression literals.
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- Don't use the `arguments` object.
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- Don't use primitive type aliases or misleading types.
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- Don't use the comma operator.
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- Don't use empty type parameters in type aliases and interfaces.
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- Don't write functions that exceed a given Cognitive Complexity score.
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- Don't nest describe() blocks too deeply in test files.
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- Don't use unnecessary boolean casts.
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- Don't use unnecessary callbacks with flatMap.
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- Use for...of statements instead of Array.forEach.
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- Don't create classes that only have static members (like a static namespace).
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- Don't use this and super in static contexts.
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- Don't use unnecessary catch clauses.
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- Don't use unnecessary constructors.
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- Don't use unnecessary continue statements.
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- Don't export empty modules that don't change anything.
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- Don't use unnecessary escape sequences in regular expression literals.
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- Don't use unnecessary fragments.
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- Don't use unnecessary labels.
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- Don't use unnecessary nested block statements.
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- Don't rename imports, exports, and destructured assignments to the same name.
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- Don't use unnecessary string or template literal concatenation.
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- Don't use String.raw in template literals when there are no escape sequences.
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- Don't use useless case statements in switch statements.
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- Don't use ternary operators when simpler alternatives exist.
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- Don't use useless `this` aliasing.
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- Don't use any or unknown as type constraints.
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- Don't initialize variables to undefined.
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- Don't use the void operators (they're not familiar).
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- Use arrow functions instead of function expressions.
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- Use Date.now() to get milliseconds since the Unix Epoch.
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- Use .flatMap() instead of map().flat() when possible.
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- Use literal property access instead of computed property access.
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- Don't use parseInt() or Number.parseInt() when binary, octal, or hexadecimal literals work.
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- Use concise optional chaining instead of chained logical expressions.
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- Use regular expression literals instead of the RegExp constructor when possible.
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- Don't use number literal object member names that aren't base 10 or use underscore separators.
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- Remove redundant terms from logical expressions.
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- Use while loops instead of for loops when you don't need initializer and update expressions.
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- Don't pass children as props.
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- Don't reassign const variables.
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- Don't use constant expressions in conditions.
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- Don't use `Math.min` and `Math.max` to clamp values when the result is constant.
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- Don't return a value from a constructor.
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- Don't use empty character classes in regular expression literals.
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- Don't use empty destructuring patterns.
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- Don't call global object properties as functions.
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- Don't declare functions and vars that are accessible outside their block.
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- Make sure builtins are correctly instantiated.
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- Don't use super() incorrectly inside classes. Also check that super() is called in classes that extend other constructors.
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- Don't use variables and function parameters before they're declared.
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- Don't use 8 and 9 escape sequences in string literals.
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- Don't use literal numbers that lose precision.
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### React and JSX Best Practices
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- Don't use the return value of React.render.
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- Make sure all dependencies are correctly specified in React hooks.
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- Make sure all React hooks are called from the top level of component functions.
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- Don't forget key props in iterators and collection literals.
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- Don't destructure props inside JSX components in Solid projects.
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- Don't define React components inside other components.
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- Don't use event handlers on non-interactive elements.
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- Don't assign to React component props.
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- Don't use both `children` and `dangerouslySetInnerHTML` props on the same element.
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- Don't use dangerous JSX props.
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- Don't use Array index in keys.
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- Don't insert comments as text nodes.
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- Don't assign JSX properties multiple times.
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- Don't add extra closing tags for components without children.
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- Use `<>...</>` instead of `<Fragment>...</Fragment>`.
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- Watch out for possible "wrong" semicolons inside JSX elements.
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### Correctness and Safety
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- Don't assign a value to itself.
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- Don't return a value from a setter.
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- Don't compare expressions that modify string case with non-compliant values.
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- Don't use lexical declarations in switch clauses.
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- Don't use variables that haven't been declared in the document.
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- Don't write unreachable code.
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- Make sure super() is called exactly once on every code path in a class constructor before this is accessed if the class has a superclass.
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- Don't use control flow statements in finally blocks.
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- Don't use optional chaining where undefined values aren't allowed.
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- Don't have unused function parameters.
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- Don't have unused imports.
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- Don't have unused labels.
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- Don't have unused private class members.
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- Don't have unused variables.
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- Make sure void (self-closing) elements don't have children.
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- Don't return a value from a function with the return type 'void'
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- Use isNaN() when checking for NaN.
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- Make sure "for" loop update clauses move the counter in the right direction.
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- Make sure typeof expressions are compared to valid values.
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- Make sure generator functions contain yield.
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- Don't use await inside loops.
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- Don't use bitwise operators.
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- Don't use expressions where the operation doesn't change the value.
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- Make sure Promise-like statements are handled appropriately.
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- Don't use __dirname and __filename in the global scope.
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- Prevent import cycles.
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- Don't use configured elements.
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- Don't hardcode sensitive data like API keys and tokens.
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- Don't let variable declarations shadow variables from outer scopes.
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- Don't use the TypeScript directive @ts-ignore.
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- Prevent duplicate polyfills from Polyfill.io.
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- Don't use useless backreferences in regular expressions that always match empty strings.
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- Don't use unnecessary escapes in string literals.
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- Don't use useless undefined.
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- Make sure getters and setters for the same property are next to each other in class and object definitions.
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- Make sure object literals are declared consistently (defaults to explicit definitions).
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- Use static Response methods instead of new Response() constructor when possible.
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- Make sure switch-case statements are exhaustive.
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- Make sure the `preconnect` attribute is used when using Google Fonts.
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- Use `Array#{indexOf,lastIndexOf}()` instead of `Array#{findIndex,findLastIndex}()` when looking for the index of an item.
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- Make sure iterable callbacks return consistent values.
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- Use `with { type: "json" }` for JSON module imports.
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- Use numeric separators in numeric literals.
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- Use object spread instead of `Object.assign()` when constructing new objects.
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- Always use the radix argument when using `parseInt()`.
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- Make sure JSDoc comment lines start with a single asterisk, except for the first one.
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- Include a description parameter for `Symbol()`.
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- Don't use spread (`...`) syntax on accumulators.
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- Don't use the `delete` operator.
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- Don't access namespace imports dynamically.
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- Don't use namespace imports.
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- Declare regex literals at the top level.
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- Don't use `target="_blank"` without `rel="noopener"`.
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### TypeScript Best Practices
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- Don't use TypeScript enums.
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- Don't export imported variables.
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- Don't add type annotations to variables, parameters, and class properties that are initialized with literal expressions.
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- Don't use TypeScript namespaces.
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- Don't use non-null assertions with the `!` postfix operator.
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- Don't use parameter properties in class constructors.
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- Don't use user-defined types.
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- Use `as const` instead of literal types and type annotations.
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- Use either `T[]` or `Array<T>` consistently.
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- Initialize each enum member value explicitly.
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- Use `export type` for types.
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- Use `import type` for types.
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- Make sure all enum members are literal values.
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- Don't use TypeScript const enum.
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- Don't declare empty interfaces.
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- Don't let variables evolve into any type through reassignments.
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- Don't use the any type.
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- Don't misuse the non-null assertion operator (!) in TypeScript files.
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- Don't use implicit any type on variable declarations.
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- Don't merge interfaces and classes unsafely.
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- Don't use overload signatures that aren't next to each other.
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- Use the namespace keyword instead of the module keyword to declare TypeScript namespaces.
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### Style and Consistency
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- Don't use global `eval()`.
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- Don't use callbacks in asynchronous tests and hooks.
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- Don't use negation in `if` statements that have `else` clauses.
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- Don't use nested ternary expressions.
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- Don't reassign function parameters.
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- This rule lets you specify global variable names you don't want to use in your application.
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- Don't use specified modules when loaded by import or require.
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- Don't use constants whose value is the upper-case version of their name.
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- Use `String.slice()` instead of `String.substr()` and `String.substring()`.
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- Don't use template literals if you don't need interpolation or special-character handling.
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- Don't use `else` blocks when the `if` block breaks early.
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- Don't use yoda expressions.
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- Don't use Array constructors.
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- Use `at()` instead of integer index access.
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- Follow curly brace conventions.
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- Use `else if` instead of nested `if` statements in `else` clauses.
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- Use single `if` statements instead of nested `if` clauses.
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- Use `new` for all builtins except `String`, `Number`, and `Boolean`.
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- Use consistent accessibility modifiers on class properties and methods.
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- Use `const` declarations for variables that are only assigned once.
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- Put default function parameters and optional function parameters last.
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- Include a `default` clause in switch statements.
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- Use the `**` operator instead of `Math.pow`.
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- Use `for-of` loops when you need the index to extract an item from the iterated array.
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- Use `node:assert/strict` over `node:assert`.
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- Use the `node:` protocol for Node.js builtin modules.
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- Use Number properties instead of global ones.
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- Use assignment operator shorthand where possible.
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- Use function types instead of object types with call signatures.
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- Use template literals over string concatenation.
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- Use `new` when throwing an error.
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- Don't throw non-Error values.
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- Use `String.trimStart()` and `String.trimEnd()` over `String.trimLeft()` and `String.trimRight()`.
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- Use standard constants instead of approximated literals.
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- Don't assign values in expressions.
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- Don't use async functions as Promise executors.
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- Don't reassign exceptions in catch clauses.
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- Don't reassign class members.
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- Don't compare against -0.
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- Don't use labeled statements that aren't loops.
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- Don't use void type outside of generic or return types.
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- Don't use console.
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- Don't use control characters and escape sequences that match control characters in regular expression literals.
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- Don't use debugger.
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- Don't assign directly to document.cookie.
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- Use `===` and `!==`.
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- Don't use duplicate case labels.
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- Don't use duplicate class members.
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- Don't use duplicate conditions in if-else-if chains.
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- Don't use two keys with the same name inside objects.
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- Don't use duplicate function parameter names.
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- Don't have duplicate hooks in describe blocks.
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- Don't use empty block statements and static blocks.
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- Don't let switch clauses fall through.
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- Don't reassign function declarations.
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- Don't allow assignments to native objects and read-only global variables.
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- Use Number.isFinite instead of global isFinite.
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- Use Number.isNaN instead of global isNaN.
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- Don't assign to imported bindings.
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- Don't use irregular whitespace characters.
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- Don't use labels that share a name with a variable.
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- Don't use characters made with multiple code points in character class syntax.
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- Make sure to use new and constructor properly.
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- Don't use shorthand assign when the variable appears on both sides.
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- Don't use octal escape sequences in string literals.
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- Don't use Object.prototype builtins directly.
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- Don't redeclare variables, functions, classes, and types in the same scope.
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- Don't have redundant "use strict".
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- Don't compare things where both sides are exactly the same.
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- Don't let identifiers shadow restricted names.
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- Don't use sparse arrays (arrays with holes).
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- Don't use template literal placeholder syntax in regular strings.
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- Don't use the then property.
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- Don't use unsafe negation.
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- Don't use var.
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- Don't use with statements in non-strict contexts.
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- Make sure async functions actually use await.
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- Make sure default clauses in switch statements come last.
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- Make sure to pass a message value when creating a built-in error.
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- Make sure get methods always return a value.
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- Use a recommended display strategy with Google Fonts.
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- Make sure for-in loops include an if statement.
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- Use Array.isArray() instead of instanceof Array.
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- Make sure to use the digits argument with Number#toFixed().
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- Make sure to use the "use strict" directive in script files.
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### Next.js Specific Rules
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- Don't use `<img>` elements in Next.js projects.
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- Don't use `<head>` elements in Next.js projects.
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- Don't import next/document outside of pages/_document.jsx in Next.js projects.
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- Don't use the next/head module in pages/_document.js on Next.js projects.
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### Testing Best Practices
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- Don't use export or module.exports in test files.
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- Don't use focused tests.
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- Make sure the assertion function, like expect, is placed inside an it() function call.
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- Don't use disabled tests.
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## Common Tasks
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- `npx ultracite init` - Initialize Ultracite in your project
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- `npx ultracite fix` - Format and fix code automatically
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- `npx ultracite check` - Check for issues without fixing
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## Example: Error Handling
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```typescript
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// ✅ Good: Comprehensive error handling
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try {
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const result = await fetchData();
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return { success: true, data: result };
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} catch (error) {
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console.error('API call failed:', error);
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return { success: false, error: error.message };
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}
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// ❌ Bad: Swallowing errors
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try {
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return await fetchData();
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} catch (e) {
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console.log(e);
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}
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```

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