---
id: kb-2026-00098
title: ResizeObserver
schema_type: TechArticle
category: computer-science
language: en
confidence: medium
last_verified: "2026-05-28"
created_date: "2026-05-22"
generation_method: human_only
derived_from_human_seed: true
conflict_of_interest: none_declared
is_live_document: false
data_period: static
atomic_facts:
  - id: fact-computer-science-resizeobserver-001
    statement: The Resize Observer specification describes an API for observing changes to an Element size.
    source_title: Resize Observer
    source_url: https://www.w3.org/TR/resize-observer-1/
    confidence: medium
  - id: fact-computer-science-resizeobserver-002
    statement: ResizeObserver can observe content-box, border-box, and device-pixel-content-box sizes.
    source_title: Resize Observer
    source_url: https://www.w3.org/TR/resize-observer-1/
    confidence: medium
  - id: fact-computer-science-resizeobserver-003
    statement: >-
      ResizeObserverEntry exposes the observed target and size information such as contentRect, borderBoxSize,
      contentBoxSize, and devicePixelContentBoxSize.
    source_title: ResizeObserverEntry - Web APIs | MDN
    source_url: https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserverEntry
    confidence: medium
completeness: 0.86
known_gaps:
  - This public sample was manually narrowed to source-backed facts on 2026-05-28.
disputed_statements: []
primary_sources:
  - title: Resize Observer
    type: standard
    year: 2020
    url: https://www.w3.org/TR/resize-observer-1/
    institution: W3C
  - title: ResizeObserver - Web APIs | MDN
    type: documentation
    year: 2026
    url: https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserver
    institution: Mozilla
  - title: ResizeObserverEntry - Web APIs | MDN
    type: documentation
    year: 2026
    url: https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserverEntry
    institution: Mozilla
secondary_sources: []
updated: "2026-05-28"
---

## TL;DR

ResizeObserver lets scripts observe element size changes. This repair removes overbroad claims and keeps to the W3C interface and MDN entry documentation.

## Core Explanation

ResizeObserver is useful when a component needs to react to its own rendered size instead of only viewport size. Observations are delivered as entries that identify the target element and expose the observed box sizes.

## Further Reading

- [Resize Observer](https://www.w3.org/TR/resize-observer-1/)
- [ResizeObserver - Web APIs | MDN](https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserver)
- [ResizeObserverEntry - Web APIs | MDN](https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserverEntry)