Interactive Node Linking & Creation
Svelvet allows users to enable
  interactive node linking and creation in their diagrams. Initially, node
  linking and creation is
  not enabled
  by default. To access these features, add the
  nodeCreate
  prop to your Svelvet
  application. These do not have to be set equal to anything and can just be passed
  in. Adding these props will enable interactive node linking and creation. NOTE:
  To have full access to the node creation feature, node linking feature must also
  be passed down as a prop. Node
  anchors
  will turn red and the
  cursor
  will change to a crosshair to
  indicate that node linking or creation is
  enabled. If the user wishes to
  not create a node after clicking on the
  anchor simply go back to that anchor
  and release the mouse click.
PS: you can also link edges!
Implementing Node Linking & Creation
Click here for a sandbox, or test it out below!