Prefer immutable data patterns
SkillWeb & browsingimmutable-patterns is a skill for AI agents that reviews JavaScript code for in-place mutations of objects and arrays. It checks scripts, client components, bundles, and runtime behavior so that fixes for shared-state bugs target the real cause. It guides the agent toward immutable data patterns such as spread copies and non-mutating array methods.
Available today. Use it from your connected AI after setup.
No other account needed.
Have a codebase with JavaScript scripts or client components to review.
Then ask your AI: use the Prefer immutable data patterns skill
What your AI can do with it
- Find places where objects or arrays are mutated in place
- Flag direct property assignments on function parameters
- Flag push and splice usage on arrays
- Replace mutations with spread operators and non-mutating methods
- Explain why mutation causes bugs in shared state
- Review scripts, client components, and browser execution paths
Getting started
- Have a codebase with JavaScript scripts or client components to review.
- Add the immutable-patterns skill to the agent's available skills.
- Ask the agent to review the code for in-place mutations of objects and arrays.
- Apply the suggested immutable replacements and verify the change in the browser.
What this skill tells your AI
The instructions your AI receives, as published by thedaviddias/front-end-checklist in skills/immutable-patterns/SKILL.md and read by ahel’s review.
Mutating shared objects makes it impossible to track where a value changed. When you update state immutably, each version of the data is a separate object — you can compare references to detect changes, time-travel debug, and know exactly which part of your code changed the data.
Quick Reference
- Use spread (...) to create modified copies of objects and arrays
- Prefer map(), filter(), and reduce() over push(), splice(), and direct assignment
- Use Object.freeze() for configuration objects that should never change
- Immutability is especially important in state management (Redux, Zustand, Signals)
Check
Find all places in this code where objects or arrays are mutated in place. Flag direct property assignments on function parameters and push/splice on arrays.
Fix
Replace in-place mutations with immutable patterns using spread operators and non-mutating array methods.
Explain
Explain immutable data patterns, why mutation causes bugs in shared state, and how spread and array methods enable immutability.
Code Review
Review scripts, client components, and browser execution paths related to Prefer immutable data patterns. Flag exact imports, event handlers, runtime side effects, or blocking operations that violate the rule, and state how the change should be verified in the browser.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/en/rules/javascript/immutable-patterns
Signals
- GitHub stars
- 74k
- Forks
- 7k
- Last commit
- Aug 2026
Questions
- What does the skill check for?
- It finds all places where objects or arrays are mutated in place, flags direct property assignments on function parameters, and flags push or splice on arrays.
- How are fixes applied?
- In-place mutations are replaced with immutable patterns using spread operators and non-mutating array methods like map, filter, and reduce.
- Does it explain the reasoning behind the rule?
- Yes. It explains immutable data patterns, why mutation causes bugs in shared state, and how spread and array methods enable immutability.
- When is immutability especially important?
- In state management, including Redux, Zustand, and Signals, where comparing references helps detect changes and track which code changed the data.
Advanced
- Item type
- skill
- Key
immutable-patterns- Source
- github.com/thedaviddias/front-end-checklist