Is resize-observer-polyfill still necessary in modern browsers?

It depends on your browser support targets; for projects needing IE9-10 or older versions of Safari, yes, but for apps targeting Chrome 64+, Firefox 69+, or Edge 79+ with native ResizeObserver, you can skip it to reduce bundle size.

How does resize-observer-polyfill compare to other polyfills like resize-observer?

This polyfill is spec-compliant and uses MutationObserver without polling, making it more performant and accurate than alternatives that rely on scroll or iframe strategies, but it has the ~20ms delay trade-off.

How to use resize-observer-polyfill with React or Vue?

Import it as a ponyfill in component lifecycle methods; for React, use it in useEffect to observe refs, and clean up with disconnect() to avoid memory leaks, similar to native ResizeObserver integration.

Does resize-observer-polyfill work with Internet Explorer 9?

Yes, it supports IE9 and IE10 using Mutation Events as a fallback, though with potential performance differences noted in the README's observation strategy section.

What are the performance impacts of using this polyfill?

Minimal in most cases due to no polling, but the MutationObserver approach can slow down DOM-heavy operations by 1-3% in IE, as per the README's benchmarks, so test in target browsers.

How to observe hover state changes with resize-observer-polyfill?

You can't directly; the README suggests adding a short CSS transition to trigger transitionend events as a workaround, which adds complexity for dynamic pseudo-classes.

Open-Awesome

resize-observer-polyfill

MITJavaScript1.5.1

A polyfill for the Resize Observer API that uses MutationObserver and Mutation Events without polling.

GitHub

1.7k stars130 forks0 contributors

What is resize-observer-polyfill?

ResizeObserver Polyfill is a JavaScript library that implements the Resize Observer API for browsers that don't support it natively. It allows developers to detect when an element's size changes, such as due to layout shifts, CSS animations, or dynamic content, without using inefficient polling techniques. The polyfill follows the official specification and provides a near-native experience.

Target Audience

Frontend developers building responsive web applications that need to react to element size changes across multiple browsers, including older versions of Internet Explorer (IE9+).

Value Proposition

Developers choose this polyfill because it's lightweight, spec-compliant, and uses efficient DOM mutation observers instead of polling. It handles edge cases like CSS transitions and doesn't require modifying observed elements, making it a reliable drop-in solution for cross-browser ResizeObserver support.

Overview

A polyfill for the Resize Observer API

Use Cases

Best For

Adding responsive behavior to elements that change size dynamically
Building cross-browser compatible applications that require element resize detection
Observing size changes during CSS transitions and animations
Supporting older browsers like IE9 and IE10 with modern resize observation
Implementing custom layouts that react to container or content dimension changes
Creating reusable components that need to adapt to their parent container's size

Not Ideal For

Applications requiring real-time, sub-20ms resize notifications for interactive elements like live dashboards or gaming interfaces
Projects exclusively targeting modern browsers with native ResizeObserver support (e.g., Chrome 64+, Firefox 69+), where the polyfill adds unnecessary overhead
Use cases where observing size changes from CSS pseudo-classes like :hover is critical without implementing additional transition-based workarounds
Environments with strict performance budgets that cannot tolerate any polyfill overhead, even from a lightweight 2.44 KiB bundle

Pros & Cons

Pros

Spec-Compliant Accuracy

Follows the official Resize Observer specification closely, mimicking native browser behavior for consistent cross-browser implementation, as emphasized in the README's philosophy.

Lightweight Performance

Minified and gzipped size is only 2.44 KiB, minimizing load time and performance impact compared to polling-based alternatives.

No Polling Overhead

Relies on MutationObserver and Mutation Events to detect DOM changes, avoiding continuous layout checks that can degrade application performance.

Handles CSS Animations

Can observe size changes caused by CSS transitions and animations, making it suitable for dynamic interfaces, as stated in the key features.

Cons

Notification Delay

Admits notifications are delivered ~20ms after actual changes, which may cause jank in time-sensitive applications like real-time visualizations.

Limited Pseudo-Class Support

Cannot track changes from dynamic CSS pseudo-classes like :hover without manual workarounds, a acknowledged limitation that restricts use in highly interactive UIs.

Deprecated Global Version

The global version (dist/ResizeObserver.global) is deprecated and will be removed, forcing legacy setups to migrate and potentially breaking existing implementations.

Frequently Asked Questions

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