screen.availHeight:
This denotes the available height in the screen, i.e., the height of the users screen. Thus, if the screen resolution of the users screen is 1366 768 pixels and the height of the taskbar is 25 pixels, this property will return 768 - 25 = 743 pixels.

Example :-

console.log("Available Height: " + screen.availHeight + "px");

screen.availWidth:
The property will returns the available width of screen.

Example:-

console.log("Avail Width: "+ screen.availWidth + "px");

screen.height:
This property denotes the actual height of the screen.

Example:-

console.log("Screen Height: "+ screen.height + "px");

screen.width:
This property denotes the actual width of the users screen.

Example:-

console.log("Screen Height: "+ screen.width + "px");