Window.screenTop
Window.screenTop
只读属性返回垂直距离,单位是 CSS 像素,从用户浏览器的上边界到屏幕最顶端。
备注: screenTop
is an alias of the older Window.screenY
property. screenTop
was originally supported only in IE but was introduced everywhere due to popularity.
语法
topWindowPos = window.screenTop
返回值
A number equal to the number of CSS pixels from the top edge of the browser viewport to the top edge of the screen.
例子
In our screenleft-screentop example, you'll see a canvas onto which has been drawn a circle. In this example we are using screenLeft
/screenTop
plus Window.requestAnimationFrame()
to constantly redraw the circle in the same physical position on the screen, even if the window position is moved.
initialLeft = window.screenLeft + canvasElem.offsetLeft;
initialTop = window.screenTop + canvasElem.offsetTop;
function positionElem() {
let newLeft = window.screenLeft + canvasElem.offsetLeft;
let newTop = window.screenTop + canvasElem.offsetTop;
let leftUpdate = initialLeft - newLeft;
let topUpdate = initialTop - newTop;
ctx.fillStyle = 'rgb(0, 0, 0)';
ctx.fillRect(0, 0, width, height);
ctx.fillStyle = 'rgb(0, 0, 255)';
ctx.beginPath();
ctx.arc(leftUpdate + (width/2), topUpdate + (height/2) + 35, 50, degToRad(0), degToRad(360), false);
ctx.fill();
pElem.textContent = 'Window.screenLeft: ' + window.screenLeft + ', Window.screenTop: ' + window.screenTop;
window.requestAnimationFrame(positionElem);
}
window.requestAnimationFrame(positionElem);
Also in the code we include a snippet that detects whether screenLeft
is supported, and if not, polyfills in screenLeft
/screenTop
using Window.screenX
/Window.screenY
.
if(!window.screenLeft) {
window.screenLeft = window.screenX;
window.screenTop = window.screenY;
}
规范
Specification |
---|
CSSOM View Module # dom-window-screentop |
浏览器兼容性
BCD tables only load in the browser