Viewport: How to get viewport size.

jQuery(window).width() uses document.documentElement.clientWidth and is regarded as cross-browser compatible. Directly using .clientWidth is faster and equally compatible. The tables below compare these live against the inner/outer methods to determine the most accurate method: verge wins because itnormalizes browser nuances to accurately match @media breakpoints.

Device: How to get device size.

Use window.screen.width for device width and window.screen.height for device height..availWidth and .availHeight give you the device size minus UI taskbars. (Try on an iPhone.) Device size is static and does not change when the page is resized or rotated.

Document: How to get document size.

Document size methods are often needed in scrolling apps. Note the difference between jQuery(document).width() and the native properties (especially when the window is wider than the max-width of the body). jQuery uses the Math.max of 5 numbers to calculate this. For decent cross-browser support, the Math.max of the 3 document.documentElement properties seems to suffice.