Code Splitting
Testing & Qualitycode-splittingCode Splitting is an Agent Skill for testing & quality published in the thedaviddias/Front-End-Checklist repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.
Use when reviewing large SPA bundles, new dependency additions, or routes that feel slow to hydrate. Focus on code that is not required for the initial view and can move behind route transitions, user interaction, or viewport-based loading.
How to use this skill
Bring this guide into your coding agent with a prompt tailored to the tool you use.
- Open your project in Codex.
- Copy and paste the prompt below.
- Review files and risks before approving any action.
Inspect the Agent Skill at https://github.com/thedaviddias/Front-End-Checklist/blob/HEAD/skills/code-splitting/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/code-splitting, but wait for my approval before writing files or running scripts.
Copying this prompt does not install or run the skill. Review third-party files before use.
Split large JavaScript bundles
A 500 KB JavaScript bundle blocks page interactivity for 3–5 seconds on a mid-range mobile device even after the bytes arrive — JS must be parsed and compiled before execution. Code splitting means users only download and parse the code they actually need for the current page, dramatically improving Time to Interactive.
Quick Reference
- Use dynamic import() to load code only when it's actually needed
- Split routes in SPAs so each page loads only its own code
- Lazy-load heavy third-party libraries (chart libraries, rich text editors)
- Analyze your bundle with a visualizer to find what to split
Check
Identify any large third-party imports or feature modules in this file that could be loaded lazily with dynamic import() instead of statically.
Fix
Convert the identified static imports to dynamic imports using import() and add appropriate loading states.
Explain
Explain JavaScript code splitting, how dynamic import() works, and how to implement route-based splitting in a SPA.
Code Review
Inspect route modules, heavy feature imports, and third-party libraries loaded on initial render. Flag dependencies that can move behind import(), route boundaries, or user-triggered flows without breaking the first meaningful paint.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/en/rules/javascript/code-splitting