Comprehensive Front‑End Code Review Checklist and Best Practices

Key Review Metrics

Front‑end code review mainly focuses on the following aspects:

Code Quality : Is the code concise, readable, and maintainable? Does it follow consistent style guidelines such as ESLint or Prettier? Functionality : Does the code implement the expected behavior without bugs or logical errors? Performance Optimization : Are unnecessary renders avoided, appropriate data structures used, and heavy resources split or lazy‑loaded? Security : Are there potential XSS, CSRF, or other security risks? Testability : Is the code easy to unit‑test and integration‑test? Readability : Are variable, function, class, and file names semantic? Are comments and documentation sufficient? Reusability : Is the code modular and reusable? Compatibility : Does the code work across different browsers and devices? Mnemonic: "功性读复全兼测" (Quality, Function, Performance, Security, Testability, Readability, Reusability, Compatibility).

Function Review

Comments must be clear; TypeScript types should be explicit so that users understand the code effortlessly.

Provide matching unit tests ("paired unit tests") to avoid any excuse for missing coverage.

Performance Review

Typical, visible performance issues in front‑end code include:

Over‑rendering : Avoid re‑rendering when props have not changed; use shouldComponentUpdate , React.PureComponent , or useEffect as needed. Excessive DOM manipulation : Prefer virtual DOM or DocumentFragment for batch updates. Too many network requests : Apply caching, pre‑loading, or lazy‑loading techniques. Large JavaScript bundles : Use code‑splitting and lazy‑loading. Unoptimized images/media : Compress images, choose proper formats, and serve via CDN. Render‑blocking CSS/JS : Adopt non‑blocking loading strategies such as async, defer, inline critical CSS, or media queries.

Non‑blocking CSS/JS Loading

When the browser encounters <link> or <script> tags, it stops parsing HTML to download and execute those resources, causing render‑blocking.

Strategies:

Async JavaScript : Use the async attribute so the script loads in parallel and executes when ready (only for scripts that do not depend on the DOM).

<script async src="script.js"></script>

Defer JavaScript : Use the defer attribute to execute after the DOM is fully parsed (suitable for DOM‑dependent scripts).

<script defer src="script.js"></script>

Inline Critical CSS : Embed the CSS required for the first paint directly in the HTML.

<style>
  /* Critical CSS */
</style>

Media Queries : Load device‑specific styles only when needed.

<link rel="stylesheet" media="(max-width: 600px)" href="mobile.css">

Readability Review

Key points to check:

Semantic naming for variables, functions, classes, files, and folders. Clear comments. Comprehensive documentation. Explicit TypeScript type declarations.

Reusability Review

Assess whether the code can be packaged as:

Function

Class

Directive

Hook

Component

Module

Security Review

Front‑end security review should cover:

XSS : Ensure user input is properly escaped; avoid dangerouslySetInnerHTML (React) or v-html (Vue) unless absolutely necessary. CSRF : Verify that all POST requests include a CSRF token. Clickjacking : Set appropriate X-Frame-Options headers. Content Tampering : Serve all resources over HTTPS. Input Validation : Validate on both client and server to prevent injection attacks. Sensitive Information Leakage : Avoid exposing secrets in URLs, error messages, or logs. Dependency Security : Keep third‑party libraries up‑to‑date and check for known vulnerabilities.

Clickjacking

The X-Frame-Options HTTP response header controls whether a page can be embedded in another page.

Possible values: DENY: Disallow embedding anywhere. SAMEORIGIN: Allow only same‑origin pages. ALLOW-FROM uri: Allow a specific origin (deprecated and not widely supported).

Always set a valid X-Frame-Options header to mitigate clickjacking.

Compatibility Review

Compatibility checks should include:

Browser Compatibility : Ensure the code works in all supported browsers; use polyfills or vendor prefixes when needed. Device Compatibility : Verify behavior on various operating systems, screen sizes, and resolutions. Responsive Design : Confirm the UI adapts to mobile, tablet, and desktop layouts. Accessibility : Follow WAI‑ARIA standards so assistive technologies can use the app. Internationalization & Localization : Support multiple languages, date, time, and number formats. Performance on Low‑End Devices/Networks : Ensure acceptable experience under constrained conditions.

What Is a Polyfill?

A polyfill is a piece of JavaScript that implements missing browser features, allowing developers to use modern APIs without breaking older browsers.

Example: Array.prototype.includes is not supported in IE, so a polyfill can add it:

if (!Array.prototype.includes) {
  Array.prototype.includes = function(element) {
    return this.indexOf(element) !== -1;
  };
}

In practice, developers usually rely on libraries such as core-js or polyfill.io.

Configuring Polyfills with Babel

Install core-js and @babel/preset-env.

npm install --save core-js
npm install --save-dev @babel/preset-env

Add the preset to .babelrc and enable useBuiltIns with the desired corejs version.

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "useBuiltIns": "usage", // or "entry"
        "corejs": 3 // specify core‑js version
      }
    ]
  ]
}

If using entry, import the polyfills manually: import "core-js"; Further configuration may be required depending on the project.

Testability Review

Key testability aspects include:

Unit Tests : Functions should be pure and avoid global state. Integration Tests : Components must use props/state correctly and avoid direct DOM manipulation. End‑to‑End (E2E) Tests : Pages should have easily locatable elements (ids or data‑test attributes) and clear user flows. Test Coverage : All functions and branches should be covered by tests. Mocking & Stubbing : Code should expose interfaces that allow dependencies (e.g., network calls) to be mocked. Error Handling : Errors must be caught and tested.

End‑to‑End Testing Example (Cypress)

Install Cypress:

npm install cypress --save-dev
yarn add cypress --dev

Create a test file (e.g., login.spec.js) with the following content:

describe('Login Test', function() {
  it('Successfully logs in', function() {
    // Visit login page
    cy.visit('/login')

    // Fill in credentials
    cy.get('input[name=username]').type('testuser')
    cy.get('input[name=password]').type('testpassword')

    // Submit form
    cy.get('button[type=submit]').click()

    // Verify navigation to home page
    cy.url().should('include', '/home')

    // Check welcome message
    cy.get('h1').should('contain', 'Welcome, testuser')
  })
})

Run the tests with: npx cypress open The above demonstrates a basic E2E workflow; real‑world suites will be more extensive.

功性读复全兼测! OVER, 收工干饭！