Detecting if a browser is in full screen mode

Question

Is there any way of reliably detecting if a browser is running in full screen mode? I\'m pretty sure there isn\'t any browser API I can query, but has anyone worked it out b

Answer 1

While searching high & low I have found only half-solutions. So it's better to post here a modern, working approach to this issue:

var isAtMaxWidth = (screen.availWidth - window.innerWidth) === 0;
var isAtMaxHeight = (screen.availHeight - window.outerHeight <= 1);
if (!isAtMaxWidth || !isAtMaxHeight) {
       alert("Browser NOT maximized!");
}

Tested and working properly in Chrome, Firefox, Edge and Opera* (*with Sidebar unpinned) as of 10.11.2019. Testing environment (only desktop):

CHROME - Ver. 78.0.3904.97 (64-bit)
FIREFOX - Ver. 70.0.1 (64-bit)
EDGE - Ver. 44.18362.449.0 (64-bit)
OPERA - Ver. 64.0.3417.92 (64-bit)
OS - WIN10 build 18362.449 (64-bit)

Resources:

• https://developer.mozilla.org/en-US/docs/Web/API/Screen/availWidth
• https://developer.mozilla.org/en-US/docs/Web/API/Window/innerWidth
• https://developer.mozilla.org/en-US/docs/Web/API/Screen/availHeight
• https://developer.mozilla.org/en-US/docs/Web/API/Window/outerHeight