link distance between 2 node

how to add set distance between 2 nodes?
the distance between 2 nodes should be different
each link has its own distance
like this
```
links: [
    {source:  0, target:  1, distance: 20 },
    {source:  0, target:  2, distance: 40},
    {source:  0, target:  3, distance: 80}
  ]

```

how to access distance property?
