Enhancing inputs with JavaScript (without fighting the browser)
Browsers already provide validation, focus management, and semantics for form controls. JavaScript should enhance these behaviors, not replace them. Keep scripts small, opt‑in, and resilient to failures so that your forms still work when scripts load slowly or not at all.
Events that matter
input: fire on every keystroke; debounce heavy work.change: commit‑level changes for selects, checkboxes, radios.invalid: customize error handling; callreportValidity().
Progressive enhancement
Start with semantic HTML and attributes. Add behaviors—masking, live formatting, async validation—only where they improve outcomes. Avoid breaking the underlying input’s accessibility semantics.
Performance
Keep typing responsive. Batch DOM writes, avoid layout thrash, and use requestAnimationFrame for visual updates. Consider Web Workers for expensive filtering or parsing.
State & ARIA
When building custom widgets (autocomplete, sliders), mirror state with ARIA roles and properties, and maintain keyboard support. Manage focus deliberately so users never lose their place.
Use JavaScript as a scalpel, not a sledgehammer. By enhancing native controls instead of replacing them, you ship faster, more reliable forms that remain accessible to everyone.