The easiest way to determine the size and position of an element is to call its
getBoundingClientRect() method. This method returns element positions in viewport coordinates. It expects no arguments and returns an object with
properties left, right, top, and bottom. The left and top properties give the X and Y
coordinates of the upper-left corner of the element and the right and bottom properties
give the coordinates of the lower-right corner.
element.getBoundingClientRect(); // Get position in viewport coordinates
Supported everywhere.