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.


leftWindowPos = window.screenX


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


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.arc(leftUpdate + (width/2), topUpdate + (height/2) + 35, 50, degToRad(0), degToRad(360), false);

  pElem.textContent = 'Window.screenLeft: ' + window.screenLeft + ', Window.screenTop: ' + window.screenTop;



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;


Specification Status Comment
CSS Object Model (CSSOM) View Module
The definition of 'Window.screenX' in that specification.
Working Draft Initial definition.

Browser compatibility

BCD tables only load in the browser

See also