self-loop link in directed layout

function layout() {
    
    try {
        var adjacencyList = eval('adjacencyList = ' + $('#adjacency-list').val());
    } catch (e) { alert(e); }
    
    var cells = buildGraphFromAdjacencyList(adjacencyList);
    graph.resetCells(cells);
    joint.layout.DirectedGraph.layout(graph, { setLinkVertices: false });

    _.each(cells, function(cell) {
        if (!(cell instanceof joint.dia.Link)) return;

        if (cell.get('source').id === cell.get('target').id) {
            console.log('makeLoopLink');
            makeLoopLink(paper, cell);
        }
    });
}

function makeLoopLink(paper, link) {

    var linkWidth = 40;
    var preferredSide = 'top';
    
    var graph = paper.model;
    var paperRect = g.rect({x: 0, y: 0, width: paper.options.width, height: paper.options.height});
    var bbox = V(paper.findViewByModel(link.get('source').id).el).bbox(false, paper.viewport);
    var p1, p2;

    var sides = _.uniq([preferredSide, 'top', 'bottom', 'left', 'right']);
    var sideFound = _.find(sides, function(side) {

	var centre, dx = 0, dy = 0;

	switch (side) {

	  case 'top':
	    centre = g.point(bbox.x + bbox.width / 2, bbox.y - linkWidth);
	    dx = linkWidth / 2;
	    break;

	  case 'bottom':
	    centre = g.point(bbox.x + bbox.width / 2, bbox.y + bbox.height + linkWidth);
	    dx = linkWidth / 2;
	    break;

	  case 'left':
	    centre = g.point(bbox.x - linkWidth, bbox.y + bbox.height / 2);
	    dy = linkWidth / 2;
	    break;

	  case 'right':
	    centre = g.point(bbox.x + bbox.width + linkWidth, bbox.y + bbox.height / 2);
	    dy = linkWidth / 2;
	    break;
	};

	p1 = g.point(centre).offset(-dx, -dy);
	p2 = g.point(centre).offset(dx, dy);

	return paperRect.containsPoint(p1) && paperRect.containsPoint(p2);
    }, this);

    if (sideFound) link.set('vertices', [p1,p2]);
}