elementScreenQuadrant.js

    if (typeof assert !== 'function') {
        function assert(expr, message) {
            if (!Boolean(expr)) {
                throw new Error(message || 'unknown assertion error');
            }
        }
    }

    function elementScreenQuadrant(element) {
        var type = typeof (element);
        assert(type === 'object', 'element must be an object, got ' + type);
        assert(element instanceof HTMLElement, 'element must be instance of HTMLElement, got ' + element.constructor.name);
        assert(typeof element.getBoundingClientRect === 'function', 'element does not have getBoundingClientRect');

        var rect = element.getBoundingClientRect();
        var top = rect.top,
            left = rect.left,
            right = window.innerWidth - rect.right,
            bottom = window.innerHeight - rect.bottom;

        return (top > bottom ? 'bottom' : 'top') + (left > right ? 'right' : 'left');
    }