frontend-developer

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Frontend Developer

前端开发者

A senior frontend engineering skill that encodes 20+ years of web development expertise into actionable guidance. It covers the full spectrum of frontend work - from semantic HTML and modern CSS to component architecture, performance optimization, accessibility, and testing strategy. Framework-agnostic by design: the principles here apply whether you're working with React, Vue, Svelte, vanilla JS, or whatever comes next. The web platform is the foundation.

这是一项凝聚了20多年Web开发经验的高级前端工程技能，提供可落地的指导方案。它覆盖前端开发的全领域——从语义化HTML、现代CSS到组件架构、性能优化、可访问性以及测试策略。设计上与框架无关：无论你使用React、Vue、Svelte、原生JS还是未来的其他框架，这里的原则都适用。Web平台是核心基础。

When to use this skill

何时使用此技能

Trigger this skill when the user:

Asks to build, review, or optimize frontend UI code (HTML, CSS, JS/TS)
Wants to improve web performance or Core Web Vitals scores
Needs an accessibility audit or WCAG compliance guidance
Is designing component architecture or deciding on state management
Asks about testing strategy for frontend code
Wants a code review with senior-level frontend feedback
Is working with modern CSS (container queries, cascade layers, subgrid)
Needs to optimize images, fonts, or bundle size

Do NOT trigger this skill for:

Backend-only code with no frontend implications
DevOps, CI/CD, or infrastructure work unrelated to frontend delivery

当用户有以下需求时，触发此技能：

要求构建、评审或优化前端UI代码（HTML、CSS、JS/TS）
希望提升Web性能或Core Web Vitals评分
需要可访问性审计或WCAG合规性指导
正在设计组件架构或决定状态管理方案
咨询前端代码的测试策略
需要资深前端工程师的代码评审反馈
正在使用现代CSS特性（容器查询、级联层、子网格）
需要优化图片、字体或包体积

请勿在以下场景触发此技能：

仅涉及后端且与前端无关的代码
与前端交付无关的DevOps、CI/CD或基础设施工作

Key principles

核心原则

The platform is your framework - Use native HTML elements, CSS features, and Web APIs before reaching for libraries. A
```
<dialog>
```
beats a custom modal. CSS
```
:has()
```
beats a JS parent selector. The browser is remarkably capable - lean on it.
Accessibility is not a feature, it's a baseline - Every element must be keyboard navigable. Every image needs alt text. Every form input needs a label. Every color combination must meet contrast ratios. Build accessible from the start - retrofitting is 10x harder.
Measure before you optimize - Never guess at performance. Use Lighthouse, the Performance API, and real user metrics (CrUX data). Optimize the actual bottleneck, not what you assume is slow. An unmeasured optimization is just code complexity.
Test behavior, not implementation - If a refactor breaks your tests but not your app, you have bad tests. Query by role, assert visible text, simulate real user actions. Tests should prove the product works, not that the code has a certain shape.
Simplicity scales, cleverness doesn't - Prefer 3 clear lines over 1 clever line. Prefer explicit over implicit. Prefer boring patterns over novel ones. The next developer to read your code (including future you) will thank you.

以平台为框架 - 优先使用原生HTML元素、CSS特性和Web API，再考虑引入库。原生
```
<dialog>
```
优于自定义模态框，CSS
```
:has()
```
优于JS父选择器。浏览器的能力远超想象——充分利用它。
可访问性不是特性，而是基线 - 每个元素都必须支持键盘导航。每张图片都需要替代文本。每个表单输入都需要标签。每种颜色组合都必须符合对比度要求。从一开始就构建可访问的界面——后期再补成本是前期的10倍。
先测量再优化 - 永远不要凭猜测做性能优化。使用Lighthouse、Performance API和真实用户数据（CrUX数据）。针对实际瓶颈进行优化，而非你认为慢的部分。未经测量的优化只会增加代码复杂度。
测试行为而非实现 - 如果重构后测试失败但应用仍能正常运行，说明你的测试设计有问题。按角色查询元素，断言用户可见的文本，模拟真实用户操作。测试应验证产品可用，而非代码的实现形式。
简洁性可扩展，技巧性不可 - 优先选择3行清晰的代码，而非1行巧妙的代码。优先显式而非隐式。优先常规模式而非新颖模式。下一个阅读你代码的开发者（包括未来的你）会为此感谢你。

Core concepts

核心概念

Frontend development sits at the intersection of three disciplines: engineering (code quality, architecture, testing), design (layout, interaction, visual fidelity), and user experience (performance, accessibility, resilience).

The mental model for good frontend work is layered:

Layer 1 - Markup (HTML): The semantic foundation. Choose elements for their meaning, not their appearance. Good HTML is accessible by default, works without CSS or JS, and communicates document structure to browsers, screen readers, and search engines.

Layer 2 - Presentation (CSS): Visual design expressed declaratively. Modern CSS handles responsive layouts, theming, animation, and complex selectors without JavaScript. Push as much visual logic into CSS as possible - it's faster, more maintainable, and progressive by nature.

Layer 3 - Behavior (JavaScript/TypeScript): Interactivity, state management, data fetching, and dynamic UI. This is the most expensive layer for users (parse + compile + execute), so minimize what you ship and maximize what the platform handles natively.

Layer 4 - Quality (Testing + Tooling): Automated verification that the other three layers work correctly. Tests, linting, type checking, and performance monitoring form the safety net that lets you ship with confidence.

前端开发是三个学科的交叉领域：工程（代码质量、架构、测试）、设计（布局、交互、视觉保真度）和用户体验（性能、可访问性、鲁棒性）。

优秀前端工作的思维模型是分层的：

第一层 - 标记（HTML）： 语义化基础。根据元素的含义而非外观选择标签。优质的HTML默认具备可访问性，无需CSS或JS即可运行，能向浏览器、屏幕阅读器和搜索引擎传达文档结构。

第二层 - 表现（CSS）： 以声明式方式表达视觉设计。现代CSS无需JavaScript即可处理响应式布局、主题、动画和复杂选择器。尽可能将视觉逻辑交给CSS——它更快、更易维护，且天生支持渐进式增强。

第三层 - 行为（JavaScript/TypeScript）： 交互性、状态管理、数据获取和动态UI。这对用户来说是最昂贵的层（解析+编译+执行），因此要最小化交付的代码量，最大化利用平台原生支持的功能。

第四层 - 质量保障（测试+工具）： 自动验证前三层是否正常工作。测试、代码检查、类型校验和性能监控构成安全网，让你能自信地交付产品。

Common tasks

常见任务

1. Performance audit

1. 性能审计

Evaluate a page or component for performance issues. Start with measurable data, not hunches.

Checklist:

Run Lighthouse and note LCP (< 2.5s), INP (< 200ms), CLS (< 0.1)
Check the network waterfall for render-blocking resources
Audit bundle size - look for unused code, large dependencies, missing code splitting
Verify images use modern formats (AVIF/WebP), responsive
```
srcset
```
, and lazy loading
Check font loading strategy (
```
font-display: swap
```
, preloading, subsetting)
Look for layout shifts caused by unsized images, dynamic content, or web fonts

Load
references/web-performance.md
for deep technical guidance on each metric.

评估页面或组件的性能问题。从可测量的数据入手，而非直觉。

检查清单：

运行Lighthouse并记录LCP（<2.5秒）、INP（<200毫秒）、CLS（<0.1）
检查网络瀑布图中的渲染阻塞资源
审计包体积——查找未使用的代码、大型依赖项和缺失的代码分割
验证图片是否使用现代格式（AVIF/WebP）、响应式
```
srcset
```
和懒加载
检查字体加载策略（
```
font-display: swap
```
、预加载、子集化）
查找由未指定尺寸的图片、动态内容或Web字体导致的布局偏移

如需每个指标的深度技术指导，请加载
references/web-performance.md
。

2. Accessibility audit

2. 可访问性审计

Evaluate code for WCAG 2.2 AA compliance. Automated tools catch ~30% of issues - manual review is essential.

Checklist:

Run axe-core or Lighthouse a11y audit for automated checks
Verify semantic HTML - are
```
<nav>
```
,
```
<main>
```
,
```
<button>
```
,
```
<label>
```
used correctly?
Tab through the entire UI - is every interactive element reachable and operable?
Check color contrast ratios (4.5:1 for normal text, 3:1 for large text)
Verify all images have meaningful alt text (or empty
```
alt=""
```
for decorative images)
Test with a screen reader - do announcements make sense?
Check that
```
aria-live
```
regions announce dynamic content updates
Verify forms have visible labels, error messages, and required field indicators

Load
references/accessibility.md
for ARIA patterns and screen reader testing procedures.

评估代码是否符合WCAG 2.2 AA标准。自动化工具只能检测约30%的问题——人工评审至关重要。

检查清单：

运行axe-core或Lighthouse可访问性审计进行自动检查
验证语义化HTML——
```
<nav>
```
、
```
<main>
```
、
```
<button>
```
、
```
<label>
```
是否使用正确？
按Tab键遍历整个UI——每个交互元素是否都能被访问和操作？
检查颜色对比度（普通文本4.5:1，大文本3:1）
验证所有图片都有有意义的替代文本（装饰性图片使用空
```
alt=""
```
）
使用屏幕阅读器测试——播报内容是否合理？
检查
```
aria-live
```
区域是否能播报动态内容更新
验证表单是否有可见标签、错误提示和必填字段标识

如需ARIA模式和屏幕阅读器测试流程，请加载
references/accessibility.md
。

3. Code review (frontend-focused)

3. 前端代码评审

Review frontend code with a senior engineer's eye. Prioritize in this order:

Correctness - Does it work? Edge cases handled? Error states covered?
Accessibility - Can everyone use it? Semantic HTML? Keyboard works?
Performance - Will it be fast? Bundle impact? Render-blocking?
Readability - Can the team maintain it? Clear naming? Reasonable complexity?
Security - Any XSS vectors? innerHTML? User input rendered unsafely?

Load
references/code-quality.md
for detailed review heuristics and refactoring signals.

以资深工程师的视角评审前端代码。按以下优先级排序：

正确性 - 功能是否正常？边界情况是否处理？错误状态是否覆盖？
可访问性 - 所有人都能使用吗？是否使用语义化HTML？键盘是否能正常操作？
性能 - 运行速度够快吗？对包体积有影响吗？是否存在渲染阻塞？
可读性 - 团队是否能维护？命名是否清晰？复杂度是否合理？
安全性 - 是否存在XSS风险？是否使用
```
innerHTML
```
？用户输入是否被不安全渲染？

如需详细的评审启发式方法和重构信号，请加载
references/code-quality.md
。

4. Component architecture design

4. 组件架构设计

Design component structure for a feature or page. Apply these heuristics:

Split when a component has more than one reason to change
Don't split just because a component is long - cohesion matters more than size
Prefer composition - pass children/slots instead of configuring via props
State belongs where it's used - lift only when shared, push down when not
Decision tree for state: Form input -> local state. Filter/sort -> URL params. Server data -> server state/cache. Theme/auth -> context/global.

Load
references/component-architecture.md
for composition patterns and state management guidance.

为功能或页面设计组件结构。应用以下启发式规则：

拆分时机：当组件有多个变更理由时
不拆分的情况：不要仅因为组件代码长就拆分——内聚性比大小更重要
优先组合：传递子元素/插槽而非通过props配置
状态归属：状态应放在使用它的地方——仅在需要共享时提升，不需要时下放
状态决策树：表单输入→本地状态。筛选/排序→URL参数。服务器数据→服务器状态/缓存。主题/权限→上下文/全局状态。

如需组合模式和状态管理指导，请加载
references/component-architecture.md
。

5. Writing modern CSS

5. 编写现代CSS

Use the platform's full power before reaching for JS-based solutions.

Decision guide:

Layout -> CSS Grid (2D) or Flexbox (1D)
Responsive -> Container queries for component-level, media queries for page-level
Theming -> Custom properties +
```
light-dark()
```
+
```
color-mix()
```
Typography ->
```
clamp()
```
for fluid sizing, no breakpoints needed
Animation -> CSS transitions/animations first, JS only for complex orchestration
Specificity management ->
```
@layer
```
for ordering,
```
:where()
```
for zero-specificity resets

Load
references/modern-css.md
for container queries, cascade layers, subgrid, and new selectors.

优先利用平台的全部能力，再考虑基于JS的解决方案。

决策指南：

布局→CSS Grid（二维）或Flexbox（一维）
响应式→组件级用容器查询，页面级用媒体查询
主题→自定义属性 +
```
light-dark()
```
+
```
color-mix()
```
排版→
```
clamp()
```
实现流体尺寸，无需断点
动画→优先使用CSS过渡/动画，仅在需要复杂编排时使用JS
特异性管理→
```
@layer
```
控制顺序，
```
:where()
```
实现零特异性重置

如需容器查询、级联层、子网格和新选择器的详细内容，请加载
references/modern-css.md
。

6. Testing strategy

6. 测试策略

Design a test suite that catches bugs without slowing down development.

The frontend testing trophy (most value in the middle):

Static analysis (base): TypeScript + ESLint catch type errors and common bugs
Unit tests (small): Pure functions, utilities, data transformations
Integration tests (large - most value): Render a component, interact like a user, assert the result
E2E tests (top): Critical user flows only - signup, checkout, core workflows

Rules:

Query by
```
role
```
and
```
name
```
, not by test ID or CSS class
Assert what users see, not internal state
Mock the network (use MSW), not the components
If a test breaks on refactor but the app still works, delete the test

Load
references/testing-strategy.md
for mocking strategy, visual regression, and a11y testing.

设计一个能捕获bug且不拖慢开发速度的测试套件。

前端测试奖杯模型（中间层价值最高）：

静态分析（基础）：TypeScript + ESLint捕获类型错误和常见bug
单元测试（小范围）：纯函数、工具类、数据转换
集成测试（大范围——价值最高）：渲染组件、模拟用户交互、断言结果
端到端测试（顶层）：仅覆盖关键用户流程——注册、结账、核心工作流

规则：

按
```
role
```
和
```
name
```
查询元素，而非测试ID或CSS类
断言用户可见的内容，而非内部状态
模拟网络请求（使用MSW），而非模拟组件
如果重构后测试失败但应用仍正常运行，删除该测试

如需模拟策略、视觉回归测试和可访问性测试指导，请加载
references/testing-strategy.md
。

7. Bundle optimization

7. 包体积优化

Reduce what ships to the client.

Audit with

source-map-explorer

webpack-bundle-analyzer

Replace large libraries with smaller alternatives (e.g.,
```
date-fns
```
-> native
```
Intl
```
)
Use dynamic
```
import()
```
for routes and heavy components
Check for duplicate dependencies in the bundle
Ensure tree shaking works - use ESM, avoid side effects in modules
Set performance budgets: < 200KB JS (compressed) for most pages

减少交付给客户端的代码量。

使用

source-map-explorer

或

webpack-bundle-analyzer

进行审计

用轻量替代方案替换大型库（例如：
```
date-fns
```
→原生
```
Intl
```
）
对路由和重型组件使用动态
```
import()
```
检查包中的重复依赖
确保Tree Shaking生效——使用ESM，避免模块产生副作用
设置性能预算：大多数页面JS压缩后<200KB

8. Progressive enhancement

8. 渐进式增强

Build resilient UIs that work across conditions.

Core content and navigation must work without JavaScript
Use
```
<form>
```
with proper
```
action
```
- it works without JS by default
Add loading states, error states, and empty states for every async operation

Respect

prefers-reduced-motion

prefers-color-scheme

, and

prefers-contrast

Handle offline gracefully where possible (service worker, optimistic UI)
Never assume fast network, powerful device, or latest browser

构建能适应各种环境的鲁棒UI。

核心内容和导航必须能在无JavaScript的情况下正常工作
使用带正确
```
action
```
的
```
<form>
```
——它默认无需JS即可运行
为每个异步操作添加加载状态、错误状态和空状态

尊重

prefers-reduced-motion

、

prefers-color-scheme

和

prefers-contrast

等用户偏好

尽可能优雅地处理离线场景（Service Worker、乐观UI）
永远不要假设网络快、设备强或浏览器是最新版本

Anti-patterns / common mistakes

反模式/常见错误

Mistake	Why it's wrong	What to do instead
Div soup	Loses all semantic meaning, breaks a11y, hurts SEO	Use `<nav>` , `<main>` , `<article>` , `<button>` , `<section>`
ARIA abuse	Adding `role="button"` to a `<div>` when `<button>` exists	Use native HTML elements first - they have built-in semantics, focus, and keyboard support
Performance theater	Lazy loading everything without measuring impact	Measure with Lighthouse/CrUX first, optimize the actual bottleneck
Testing implementation	Tests break on refactor, coupled to internal state	Test behavior - what the user sees and does, not how the code works
Premature abstraction	Shared component after 2 occurrences	Wait for the third use case, then extract with the real pattern visible
CSS avoidance	Runtime JS for styling that CSS handles natively	Modern CSS covers layout, theming, responsive design, and most animations
Ignoring the network	No loading/error states, assumes instant responses	Every async operation needs loading, error, and empty states
Bundle blindness	Never checking what ships to users	Audit bundle regularly, set performance budgets, check before adding deps
A11y as afterthought	Bolting on accessibility at the end	Build accessible from the start - semantic HTML, keyboard nav, ARIA where needed
Overengineering state	Global state for everything	Use local state by default, URL params for shareable state, server cache for API data
Emojis as UI icons	Render inconsistently across OS/browsers, unstyled, break a11y and theming	Use SVG icon libraries: Lucide React, React Icons, Heroicons, Phosphor, or Font Awesome

错误行为	问题所在	替代方案
Div标签堆砌	失去所有语义化含义，破坏可访问性，损害SEO	使用 `<nav>` 、 `<main>` 、 `<article>` 、 `<button>` 、 `<section>` 等语义化标签
滥用ARIA	给 `<div>` 添加 `role="button"` ，而原生 `<button>` 已存在	优先使用原生HTML元素——它们自带语义化、焦点和键盘支持
伪性能优化	不加测量就对所有内容做懒加载	先用Lighthouse/CrUX测量，针对实际瓶颈优化
测试实现细节	重构后测试失败，与内部状态耦合	测试行为——用户看到的内容和执行的操作，而非代码的实现方式
过早抽象	出现2次就提取共享组件	等出现第三个用例，明确真实模式后再提取
回避CSS	用运行时JS处理CSS原生就能实现的样式	现代CSS覆盖布局、主题、响应式设计和大多数动画
忽略网络情况	没有加载/错误状态，假设响应即时	每个异步操作都需要加载、错误和空状态
无视包体积	从不检查交付给用户的代码内容	定期审计包体积，设置性能预算，添加依赖前先检查
可访问性事后补	最后才考虑可访问性	从一开始就构建可访问的界面——语义化HTML、键盘导航、必要时使用ARIA
过度设计状态	所有状态都用全局状态	默认使用本地状态，可共享的状态用URL参数，服务器数据用服务器状态/缓存，主题/权限用上下文/全局状态
用emoji做UI图标	在不同系统/浏览器中渲染不一致，无样式，破坏可访问性和主题适配	使用SVG图标库：Lucide React、React Icons、Heroicons、Phosphor或Font Awesome

Gotchas

注意事项

CSS class-based queries in tests break on refactor - Using
```
getByClassName
```
or querying by CSS selectors couples tests to implementation. When you rename a class, tests fail even though the UI still works. Always query by
```
role
```
,
```
label
```
, or visible text.
Third-party bundle size is invisible until it's catastrophic - Adding a dependency like
```
moment.js
```
or a UI component library can triple your bundle silently. Run
```
source-map-explorer
```
or
```
webpack-bundle-analyzer
```
before merging any PR that adds a new
```
npm install
```
.
ARIA roles on wrong elements break screen readers worse than no ARIA - Adding
```
role="button"
```
to a
```
<div>
```
makes screen readers announce "button" but keyboard users still can't Tab to it or activate it with Enter/Space. Use
```
<button>
```
or add both
```
tabindex="0"
```
and a
```
keydown
```
handler. Incomplete ARIA is worse than none.
CSS container queries require a containment context on the parent - A container query will silently never fire if the parent element doesn't have
```
container-type
```
set. Adding
```
container-type: inline-size
```
to the wrong ancestor (e.g., body) changes layout behavior unexpectedly. Always set the containment on the direct parent of the component.
Lazy loading below-the-fold images is fine; lazy loading LCP images kills performance - Adding
```
loading="lazy"
```
to every image is cargo-cult optimization. The Largest Contentful Paint image must load eagerly (or use
```
fetchpriority="high"
```
). Lazy-loading the LCP image can drop your LCP score by seconds.

测试中基于CSS类的查询会在重构时失效 - 使用
```
getByClassName
```
或CSS选择器查询元素会将测试与实现耦合。重命名类后，即使UI正常工作，测试也会失败。始终按
```
role
```
、
```
label
```
或可见文本查询。
第三方依赖的包体积问题会在失控前被忽视 - 添加
```
moment.js
```
或UI组件库等依赖可能会让包体积翻倍。合并任何包含
```
npm install
```
的PR前，先运行
```
source-map-explorer
```
或
```
webpack-bundle-analyzer
```
。
错误元素上的ARIA角色比没有ARIA更破坏屏幕阅读器 - 给
```
<div>
```
添加
```
role="button"
```
会让屏幕阅读器播报“按钮”，但键盘用户仍无法通过Tab键聚焦或用Enter/Space激活。要么使用
```
<button>
```
，要么同时添加
```
tabindex="0"
```
和
```
keydown
```
事件处理。不完整的ARIA比没有更糟。
CSS容器查询需要父元素设置包含上下文 - 如果父元素未设置
```
container-type
```
，容器查询会静默失效。给错误的祖先元素（例如body）设置
```
container-type: inline-size
```
会意外改变布局行为。始终在组件的直接父元素上设置包含上下文。
懒加载首屏外的图片没问题，但懒加载LCP图片会严重影响性能 - 给所有图片添加
```
loading="lazy"
```
是盲目跟风优化。最大内容绘制（LCP）图片必须优先加载（或使用
```
fetchpriority="high"
```
）。懒加载LCP图片会让LCP评分下降数秒。

References

参考文档

For detailed guidance on specific topics, load the relevant reference file:

```
references/web-performance.md
```
- Core Web Vitals, rendering, bundle optimization, caching, images, fonts
```
references/accessibility.md
```
- WCAG 2.2, semantic HTML, ARIA patterns, keyboard navigation, screen reader testing
```
references/modern-css.md
```
- Container queries, cascade layers, subgrid, :has()/:is(), view transitions
```
references/component-architecture.md
```
- Composition patterns, state management, render optimization, design systems
```
references/testing-strategy.md
```
- Testing trophy, integration tests, visual regression, a11y testing, mocking
```
references/code-quality.md
```
- Code review heuristics, refactoring signals, TypeScript patterns, security, linting

Only load a reference file when the current task requires that depth - they are detailed and will consume context.

如需特定主题的详细指导，请加载相关参考文件：

```
references/web-performance.md
```
- Core Web Vitals、渲染、包体积优化、缓存、图片、字体
```
references/accessibility.md
```
- WCAG 2.2、语义化HTML、ARIA模式、键盘导航、屏幕阅读器测试
```
references/modern-css.md
```
- 容器查询、级联层、子网格、:has()/:is()、视图过渡
```
references/component-architecture.md
```
- 组合模式、状态管理、渲染优化、设计系统
```
references/testing-strategy.md
```
- 测试奖杯模型、集成测试、视觉回归、可访问性测试、模拟
```
references/code-quality.md
```
- 代码评审启发式方法、重构信号、TypeScript模式、安全、代码检查

仅当当前任务需要深度指导时才加载参考文件——这些文件内容详细，会占用上下文资源。

Companion check

配套技能检查

On first activation of this skill in a conversation: check which companion skills are installed by running
ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null
. Compare the results against the
recommended_skills
field in this file's frontmatter. For any that are missing, mention them once and offer to install:
npx skills add AbsolutelySkilled/AbsolutelySkilled --skill <name>
Skip entirely if
recommended_skills
is empty or all companions are already installed.

在对话中首次激活此技能时：运行
ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null
检查已安装的配套技能。将结果与本文件前置元数据中的
recommended_skills
字段对比。对于缺失的技能，提及一次并提供安装命令：
npx skills add AbsolutelySkilled/AbsolutelySkilled --skill <name>
如果
recommended_skills
为空或所有配套技能已安装，则跳过此步骤。