The read-only scrollY
property of the Window
interface returns the number of pixels that the document is currently scrolled vertically.
This value is subpixel precise in modern browsers, meaning that it isn't necessarily a whole number. You can get the number of pixels the document is scrolled horizontally from the scrollX
property.
In practice, the returned value is a double-precision floating-point value with the range of 2^(-1022) to 2^(+1023). It indicates the number of pixels the document is currently scrolled vertically from the origin, where a positive value means the content is scrolled to upward. If the document is rendered on a subpixel-precise device, then the returned value is also subpixel-precise and may contain a decimal component. If the document isn't scrolled at all up or down, then scrollY
is 0.
Note: If you need an integer value, you can use Math.round()
to round it off.
In more technical terms, scrollY
returns the Y coordinate of the top edge of the current viewport. If there is no viewport, the returned value is 0.
if (window.scrollY) {
window.scroll(0, 0);
}
window.scrollByPages(1);
Use this property to check that the document hasn't already been scrolled when using relative scroll functions such as scrollBy()
, scrollByLines()
, or scrollByPages()
.
The pageYOffset
property is an alias for the scrollY
property:
window.pageYOffset === window.scrollY;