Window.screenX

The Window.screenX read-only property returns the horizontal distance, in CSS pixels, of the left border of the user's browser viewport to the left side of the screen.

Note: An alias of screenX was implemented across modern browsers in more recent times — Window.screenLeft. This was originally supported only in IE but was introduced everywhere due to popularity.

Syntax

leftWindowPos = window.screenX

Returns

A number equal to the number of CSS pixels from the left edge of the browser viewport to the left edge of the screen.

Examples

In our screenleft-screentop (source code) example, you'll see a canvas onto which has been drawn a circle. In this example we are using Window.screenLeft/Window.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);

These work in exactly the same way as screenX/screenY.

Also in the code we include a snippet that detects whether screenLeft is supported, and if not, polyfills in screenLeft/screenTop using screenX/screenY.

if(!window.screenLeft) {
  window.screenLeft = window.screenX;
  window.screenTop = window.screenY;
}

Specifications

Specification
CSSOM View Module (CSSOM View) # dom-window-screenx

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`screenX`	1	12	1 Before Firefox 28, Gecko was using device pixels instead of CSS pixels; in other words, it was assuming a value of `screenPixelsPerCSSPixel` of 1 for any device.	9	≤12.1	1	1	18	4 Before Firefox 28, Gecko was using device pixels instead of CSS pixels; in other words, it was assuming a value of `screenPixelsPerCSSPixel` of 1 for any device.	≤12.1	1	1.0