in src/helpers/edge-helpers.js [247:267]
export function getArrowSize(viewWrapperElem: HTMLDivElement) {
const defEndArrowElement: any = viewWrapperElem.querySelector(
`defs>marker>.arrow`
);
const arrowRect = defEndArrowElement.getBoundingClientRect();
const size = {
bottom: arrowRect.bottom,
top: arrowRect.top,
// Firefox doesn't calculate width and height, so we need to pull
// from the attributes.
height: arrowRect.height || defEndArrowElement.getAttribute('height'),
width: arrowRect.width || defEndArrowElement.getAttribute('width'),
left: arrowRect.left,
right: arrowRect.right,
y: arrowRect.y,
x: arrowRect.x,
};
return size;
}