windowscrollBy

Window.scrollBy is a JavaScript method that scrolls the document by a specified amount relative to the current scroll position. It is invoked on the global window object and affects the main browsing context’s scroll position.

The method can be used in two forms. The two-argument form, window.scrollBy(dx, dy), scrolls horizontally by dx pixels and vertically by dy pixels. A positive value moves the page right or down, while a negative value moves it left or up. The newer form, window.scrollBy(options), accepts a single object with properties such as left, top, and behavior. The left and top values correspond to horizontal and vertical offsets, and behavior can be "auto" (default) or "smooth" to animate the scrolling.

In either form, the function returns undefined. It synchronously updates the document’s scroll position and may trigger scroll-related events, such as the window’s scroll event. If the page is already at a boundary (top or bottom), scrolling may have no visible effect.

Examples:

- window.scrollBy(0, 100) scrolls downward by 100 pixels.

- window.scrollBy(-50, 0) scrolls left by 50 pixels.

- window.scrollBy({ left: 0, top: 200, behavior: 'smooth' }) scrolls down smoothly by 200 pixels.

Notes and compatibility: Window.scrollBy is widely supported in modern browsers. The object-form option is not universally supported in older browsers, so developers may implement feature checks or fallbacks. The method scrolls the window as a whole; to scroll a specific element, Element.scrollBy can be used (for that element’s own scrollable area). It differs from scrollTo, which moves to an absolute position rather than relative offsets.