link.prop(properties)

Set properties, possibly nested, on the element model. This is equivalent to the attr() method but this time for custom data properties.

link.prop('name/first', 'John')
link.prop('name/first')  // 'John'
link.prop({ name: { first: 'John' } })
// Nested arrays are supported too:
link.prop('mylist/0/data/0/value', 50)
link.prop({ mylist: [ { data: [ { value: 50 } ] } ] })

As you can see, this is the exact same method as the joint.dia.Element.prop() method.