---
source: https://iinventedlight.com/library/notes/react-when-not-to-use-effect.md
title: "When you might not need an Effect"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "CC BY 4.0 (reactjs/react.dev LICENSE-DOCS); prose restates cited source lines in own words"
license_family: react-docs-ccby
attribution: "Summary by iinventedlight (AI-assisted). Sources: React docs (react.dev), You Might Not Need an Effect – React, CC BY 4.0 (reactjs/react.dev LICENSE-DOCS); React docs (react.dev), Keeping Components Pure – React, CC BY 4.0 (reactjs/react.dev LICENSE-DOCS)."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-06
status: published
checked_on: 2026-11-06
as_of: 2026-11-06
confidence: medium
untested: "No React code was run for this note; only the fetched documentation pages were read."
category: coding-references
topic_area: "code-web: effects guidance"
tags: [react, effects, derived-state]
client: Librarian
sources:
  - id: S1
    title: "You Might Not Need an Effect – React"
    publisher: React docs (react.dev)
    url: https://react.dev/learn/you-might-not-need-an-effect
    accessed: 2026-11-06
    license: "CC BY 4.0 (reactjs/react.dev LICENSE-DOCS)"
  - id: S2
    title: "Keeping Components Pure – React"
    publisher: React docs (react.dev)
    url: https://react.dev/learn/keeping-components-pure
    accessed: 2026-11-06
    license: "CC BY 4.0 (reactjs/react.dev LICENSE-DOCS)"
---
# When you might not need an Effect

Effects are an escape hatch from the React paradigm. [S1]

## Prefer calculate during render

Filtering a list for display can be done during render instead of storing filtered results in state updated by an Effect. [S1]

If an Effect immediately updates state, React restarts the render process, which is often unnecessary work. [S1]

## Stay pure when possible

Keep rendering pure: given the same inputs, return the same result without mutating prior data. [S2]

## Claims

- id: C1
  claim: Effects are an escape hatch.
  source: S1
  evidence: "Effects are an escape hatch from the React paradigm."

- id: C2
  claim: Filtering before display is a common case.
  source: S1
  evidence: "filter a list before displaying it"

- id: C3
  claim: An Effect that sets state can restart rendering.
  source: S1
  evidence: "If your Effect also immediately updates the state"

- id: C4
  claim: Pure render returns the same result for the same inputs.
  source: S2
  evidence: "should always return the same result"

## Sources

- [S1] You Might Not Need an Effect – React. React docs (react.dev). https://react.dev/learn/you-might-not-need-an-effect . License: CC BY 4.0 (reactjs/react.dev LICENSE-DOCS). Accessed 2026-11-06.

- [S2] Keeping Components Pure – React. React docs (react.dev). https://react.dev/learn/keeping-components-pure . License: CC BY 4.0 (reactjs/react.dev LICENSE-DOCS). Accessed 2026-11-06.


License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).