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CSS can remove JavaScript from bounded presentation tasks—such as tying an animation to scrolling, adapting a component to its container, or snapping an overflowing list into place. It does not replace JavaScript for application state, data loading, or interactions that need precise event control. The useful question is not which ten properties form a definitive list: several of the strongest alternatives are CSS at-rules, selectors, or browser behaviors rather than individual properties.
When CSS can take over from JavaScript
Use CSS when the desired result is a visual response to a condition the browser already knows about: scroll progress, container width, sticky positioning, or whether a declaration is supported. That can eliminate custom event handlers and layout calculations for the presentation effect itself.
Keep JavaScript when the behavior changes application state, fetches or loads data, coordinates complex interactions, or needs exact control over when and how events occur. A CSS feature may style a state without creating or managing that state.
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Animate in response to scrolling
Scroll-driven animations attach animation progress to a scroll-based timeline. That makes them a direct option for effects such as a reading-progress indicator or a visual reveal that follows scrolling, instead of manually tracking scroll position with event listeners or intersection observations. MDN describes the CSS approach and its JavaScript counterparts in its guide to scroll-driven animation timelines.
.reading-progress {
animation: fill linear both;
animation-timeline: scroll(root block);
transform-origin: left;
}
@keyframes fill {
to { transform: scaleX(1); }
}This is for a visual effect driven by scrolling, not every task that happens during a scroll. If scrolling must trigger data loading, change application state, or follow bespoke event rules, CSS alone is not a substitute. Account for motion sensitivity: avoid essential information being conveyed only by movement, and provide a reduced-motion treatment when the animation could be uncomfortable.
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Adapt components to their own width
Container size queries let a component respond to the space available around it instead of relying only on viewport breakpoints. This is useful when the same component appears in differently sized columns, cards, or sidebars.
.card-region {
container-type: inline-size;
}
@container (min-width: 32rem) {
.card {
display: grid;
grid-template-columns: 10rem 1fr;
}
}The element that establishes the query context needs an appropriate container-type; a size query cannot simply inspect any ancestor by default. MDN explains the setup and query syntax in Using container size and style queries. JavaScript may still be appropriate if a width change must trigger nonvisual work.
Style based on scroll state
Scroll-state queries allow descendants to be styled according to conditions such as whether a container is stuck, snapped, or can scroll in a particular direction. This can replace a scroll listener whose only purpose is changing a visual hint or control.
.page {
container-type: scroll-state;
}
@container scroll-state(scrollable: top) {
.back-to-top {
visibility: visible;
}
}Scroll-state queries require a container established with container-type: scroll-state, and they are a newer feature whose support should be checked for the browsers your audience uses. MDN’s scroll-state query guide shows examples including scroll direction, snapping, and sticky positioning. They can change presentation in response to a condition; they do not implement the action performed by a control.
Let the browser handle snapping and position preservation
Scroll snapping for overflowing content
For a horizontally scrolling gallery or paged overflow region, CSS scroll snapping defines positions where scrolling should settle. The browser handles the native scrolling behavior rather than requiring script to calculate and enforce every snap position. It does not provide arbitrary carousel logic, custom state management, or data loading.
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Scroll anchoring when content is inserted
When content above the visible area changes size or is inserted, scroll anchoring is a browser mechanism that helps preserve the user’s visible position instead of letting the page appear to jump. It is not a general replacement for managing application layout or scroll behavior.
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Use CSS in view transitions, not as a replacement for their API
View transitions combine an API for transitioning between interface states or documents with CSS that styles the transition. A declaration such as view-transition-name identifies an element snapshot for separate animation. CSS handles the visual treatment, while JavaScript may still initiate or coordinate a transition and manage the application’s state.
.page-title {
view-transition-name: page-title;
}For the division between the API and its CSS styling, see MDN’s View Transition API reference. Do not treat a transition effect as a replacement for the navigation or state logic that leads to the new view.
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Gate newer CSS with feature queries
@supports lets a stylesheet test whether the browser supports a CSS declaration, so a newer effect can enhance a working baseline rather than being required for the page to function.
.card {
display: block;
}
@supports (container-type: inline-size) {
.card-region {
container-type: inline-size;
}
}A feature query is a fallback tool, not a guarantee that every browser implements every related behavior identically. Check current compatibility for the features you choose and ensure the baseline remains usable. MDN explains the syntax in Using feature queries.
Choose CSS or JavaScript by the job
| Need | Prefer CSS when | Keep JavaScript when |
|---|---|---|
| Scroll-linked visual effect | Animation progress follows a scroll timeline. | Scrolling must trigger data work, application state changes, or exact custom event handling. |
| Responsive component | Appearance depends on the component’s container size. | A size change must cause nonvisual application work. |
| Scroll or sticky hint | A visual style depends on a supported scroll-state condition. | The condition must trigger an action or coordinated application behavior. |
| Overflow navigation | Native snap positions meet the design need. | The carousel needs custom state, controls, or data loading beyond snapping. |
| Transition between views | CSS should define the visual transition for identified snapshots. | The application must initiate the transition or manage the views and their state. |
For each case, consider browser support, keyboard and assistive-technology usability, reduced-motion preferences, and what a user sees when the enhancement is unavailable. Prefer CSS when it expresses the visual rule directly and the fallback is clear; retain JavaScript where the requirement is fundamentally application logic.
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