Hereif (el instanceof SVGElement)The intention should be a capability test, but I found that the incoming element el, whether there is SVGElement on its prototype chain and whether it has getBoundingClientRect seems to have nothing to do with it. Relationship, right? Even if there is no SVGElement in the prototype chain of an element, it still has the getBoundingClientRect method. So what does the writing here mean?

    me.getRect = function(el) {

        if (el instanceof SVGElement) {
            var rect = el.getBoundingClientRect();
            return {
                top : rect.top,
                left : rect.left,
                width : rect.width,
                height : rect.height
            };
        } else {
            
            return {
                top : el.offsetTop,
                left : el.offsetLeft,
                width : el.offsetWidth,
                height : el.offsetHeight
            };
        }
    };

grateful!

CRIMX

Well-founded and convincing!