New link anchor functions can be defined in the joint.linkAnchors namespace (e.g. joint.linkAnchors.myLinkAnchor) or passed directly as a function to the linkAnchor property of link source/target (or to the defaultLinkAnchor option of a paper).

In either case, the link anchor function must return the link anchor as a Point. The function is expected to have the form function(endView, endMagnet, anchorReference, args):

endView dia.LinkView The LinkView to which we are connecting. The Link model can be accessed as endView.model; this may be useful for writing conditional logic based on link attributes.
endMagnet null (Not used) This argument is only present to ensure that the signature of custom linkAnchor methods is the same as the signature of custom anchor methods.
anchorReference g.Point A reference to another component of the link path that may be necessary to find this anchor point. If we are calling this method for a source anchor, it is the first vertex; if there are no vertices, it is the target anchor. If we are calling this method for a target anchor, it is the last vertex; if there are no vertices, it is the source anchor...
SVGElement ...if the anchor in question does not exist (yet), it is that link end's magnet. (The built-in methods usually use this element's center point as reference.)
args object An object with additional optional arguments passed to the link anchor method by the user when it was called (the args property).