Good front-end code makes a page usable and a change understandable. Judge it by the behavior it delivers, how easily someone can inspect it, and how safely it can change.
1. Readability
Use names that describe purpose and keep related markup and styles easy to find. Formatting helps, but a formatter cannot clarify an unexplained constraint. Add comments when the reason is not obvious.
2. Maintainability
Make a small edit and inspect how far it spreads. A shared template is useful when it keeps repeated behavior consistent; a global selector is risky when it unexpectedly changes unrelated pages. Record prerequisites and verify output.
3. Accessibility
Start with meaningful HTML, labeled controls and usable keyboard paths. Check error messages, focus and reduced-motion behavior. A visually tidy interface can still be difficult to use.
4. Measured performance
Inspect actual assets and interaction behavior. Optimize a large image or unnecessary dependency when evidence identifies it. Compression and a CDN help delivery in suitable configurations, but neither fixes excessive work in the browser. Local measurements and real-user performance are separate evidence.
5. Proportionate reuse
Reuse stable patterns without creating an abstraction for every similar-looking box. CSS classes, templates and components can all do this; reuse is not unique to React.
Review exercise: change one labeled form, test its behavior, and explain the diff to someone who did not watch you write it. Traffic scaling also depends on hosting and services; maintainable client code alone does not establish capacity for a million users.
Sources
Reference 1 Reference 2 provide the technical details and current compatibility information.