Browser Internals articles, tutorials, and guides

In-depth articles, tutorials, and guides on Browser Internals — covering everything from fundamentals to advanced patterns.

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The Hidden Cost of MutationObserver: What Fires It and What Happens Next

Browser Internals

MutationObserver is the standard API for watching DOM changes, but it is easy to create observers that fire far more often than expected and trigger expensive processing on every mutation. Understanding when and why it fires is essential for using it without tanking performance.

IntersectionObserver Internals: How the Browser Detects Visibility

Browser Internals

IntersectionObserver is the standard API for detecting when an element enters or leaves the viewport. Understanding how it works under the hood — and what its limitations are — helps you use it efficiently and avoid the subtle bugs that come from misunderstanding when callbacks fire.