jointjs/docs/src/joint/api/dia/attributes/port.html

JavaScript diagramming library

        <p>An object containing at least an <code>id</code> property. This property uniquely identifies the port.
            If a link gets connected to a <a href="#dia.attributes.magnet">magnet</a> that has also a <code>port</code>
            object defined, the <code>id</code> property of the port object will be copied to the <code>port</code> property
            of the source/target of the link.</p>