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CSS can take JavaScript out of presentation tasks such as tying an animation to scroll progress, adapting a component to its own width, or snapping a scrolling panel into place. It does not replace JavaScript for application state, data loading, or arbitrary interaction logic—and several tools in this article are CSS at-rules or selectors, not properties.
Which JavaScript work can CSS take over?
Use CSS when the desired result is a visual response to a condition the browser already knows: scroll position, a component’s available space, a snap point, or whether a declaration is supported. This can remove event handlers and layout calculations written only to produce that presentation.
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Keep JavaScript when the interface must manage application state, fetch or transform data, coordinate custom actions, or respond with exact event-driven behavior. The practical question is not whether CSS is newer, but whether the requirement is styling or logic.
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1. Tie animation progress to scrolling
Scroll-driven animations connect keyframe progress to a scroll-based timeline. CSS features such as animation-timeline and scroll-timeline can drive a visual progress or reveal effect without scripting scroll position. MDN notes that JavaScript alternatives may rely on scroll event listeners or IntersectionObserver tracking on the main thread. That makes CSS a bounded option for scroll-driven visuals, not a reason to remove every scroll listener. MDN’s scroll-driven animation timelines guide shows timelines driven by scroll() and named scroll timelines.
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For example, a progress indicator whose appearance follows document scrolling is a styling problem. A control that must update application data or trigger a custom action at a particular point still needs logic. Account for reduced-motion preferences and provide a useful experience when the animation feature is unavailable.
2. Adapt a component to its own width
Viewport media queries answer questions about the viewport. Container size queries let a component respond to the space available to its containing context, which is useful when the same component appears in differently sized layouts.
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Declare a suitable query context with container-type, then write an @container condition for the layout change. Without an appropriately configured container, a size query has no intended component context. See MDN’s guide to container size and style queries.
3. Style descendants from scroll state
Scroll-state queries let styles respond to scroll conditions, including whether a container is snapped or whether an element is sticky. A scroll-state query container uses container-type: scroll-state; descendants can then be styled within an @container condition. This can replace a script that observes scrolling merely to show or adjust a visual hint. MDN demonstrates a back-to-top link becoming visible when the page can scroll toward its top edge. Read the scroll-state query guide for the supported conditions and syntax.
Use this for presentation tied to a browser-reported scroll condition. If a control needs to perform an action, track complex interaction history, or coordinate app state, CSS styling alone is not a substitute for that behavior.
4. Snap overflowing content into place
CSS scroll snapping defines positions where content can settle inside an overflowing scroll container. It is a browser-native way to build a snapping panel or paged strip without scripting the basic position adjustment. The CSS guides collection documents scroll snap alongside other scrolling features: MDN CSS guides.
Snapping does not supply arbitrary carousel state, custom controls, or data loading. If those are part of the interface, they remain separate requirements; do not treat snap positions as a complete carousel implementation.
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Scroll anchoring is a browser mechanism that helps prevent the visible page from jumping when content is inserted or changed above the user’s current position. It addresses a layout and scrolling problem that might otherwise tempt a developer to measure and correct scroll position with JavaScript. MDN includes scroll anchoring in its CSS guides.
It is browser behavior rather than a general-purpose substitute for app-controlled scrolling. It does not decide what content to load or how an application should respond to that content.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.6. Style elements participating in a view transition
The View Transition API coordinates transitions between UI states or documents; CSS supplies styling for the transition, including view-transition-name, which identifies an element snapshot for separate animation. This can move transition presentation into CSS, but it does not eliminate JavaScript state handling in a single-page application. The API still has to participate in the change between states. MDN’s View Transition API reference describes the broader mechanism.
Use CSS for how identified elements look during a transition. Keep the code that determines which view is active and performs the underlying state change where it belongs—in the application logic.
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The @supports at-rule tests whether a browser supports a CSS declaration, letting you apply an enhancement only when its syntax is recognized. It is a way to preserve a baseline style while adding a newer effect conditionally; it is not a replacement for JavaScript feature detection when the behavior depends on JavaScript APIs. See MDN’s guide to feature queries.
For each newer feature above, check current browser compatibility for the browsers and versions your audience needs. A support query is useful only when the unsupported case still has an acceptable fallback.
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How to decide whether to remove the script
- Presentation or application logic? Prefer CSS when the browser-known condition only changes appearance or layout. Keep code for data, state, and custom actions.
- Does the feature match the requirement? Scroll snapping is not a full carousel controller; a transition name does not manage app state.
- What happens without support? Use a baseline layout or behavior that remains understandable, and progressively enhance it where appropriate.
- Can users still control motion? Review motion effects for reduced-motion needs and avoid making essential information depend on animation.
- Do you need exact event or state control? If the requirement exceeds a browser-provided styling condition, retain JavaScript for that part.
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