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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.
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
| 规范 |
|---|
| CSSOM View Module # dom-window-screentop |
浏览器兼容性
启用 JavaScript 以查看此浏览器兼容性表。