10.3 - How do I find the size of the window/browser canvas area?

While it is often asked about window size, what is more relevant is the "canvas area" of the browser.

Where supported in NN: (>NN4.0)

var winWidth = window.innerWidth; 
var winHeight = window.innerHeight;

Where supported in IE: (>IE4.0)

var winWidth = document.body.clientWidth; 
var winHeight = document.body.clientHeight;

Where supported in modern browsers:

var winWidth = document.documentElement.clientWidth; 
var winHeight = document.documentElement.clientHeight;

Where supported in DOM compliant browsers:

var winWidth, winHeight, d=document; 
if (typeof window.innerWidth!='undefined') { 
  winWidth = window.innerWidth; 
  winHeight = window.innerHeight; 
} else { 
  if (d.documentElement && 
    typeof d.documentElement.clientWidth!='undefined' && 
    d.documentElement.clientWidth!==0) { 
      winWidth = d.documentElement.clientWidth; 
      winHeight = d.documentElement.clientHeight; 
  } else { 
    if (d.body && typeof d.body.clientWidth!='undefined') {
      winWidth = d.body.clientWidth; 
      winHeight = d.body.clientHeight; 
    } 
  } 
}

Note: The dimensions can not be determined accurately until after the document has finished loading.