Window.scrollY - Web APIs 编辑

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.

Syntax

var y = window.scrollY

Value

In practice, the returned value is a double-precision floating-point value indicating 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.

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.

Example

// make sure and go down to the second page
if (window.scrollY) {
  window.scroll(0, 0);  // reset the scroll position to the top left of the document.
}

window.scrollByPages(1);

Notes

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; // always true

For cross-browser compatibility, use window.pageYOffset instead of window.scrollY. Additionally, older versions of Internet Explorer (< 9) do not support either property and must be worked around by checking other non-standard properties. A fully compatible example:

var supportPageOffset = window.pageXOffset !== undefined;
var isCSS1Compat = ((document.compatMode || "") === "CSS1Compat");

var x = supportPageOffset ? window.pageXOffset : isCSS1Compat ? document.documentElement.scrollLeft : document.body.scrollLeft;
var y = supportPageOffset ? window.pageYOffset : isCSS1Compat ? document.documentElement.scrollTop : document.body.scrollTop;

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• window.scrollX