Should forces be parameterized per node?

[mbostock]

In the new design, you pass each force the array of nodes (and in some cases links):

var simulation = d3.forceSimulation(nodes)
    .on("beforetick.charge", d3.forceManyBody(nodes))
    .on("beforetick.link", d3.forceLink(nodes, links))
    .on("beforetick.position", d3.forcePosition(nodes).position([width / 2, height / 2]))
    .on("tick", draw);

This has the benefit that you can give each force a different subset of the nodes, but it raises some questions:

1. What if I want each node’s forces to have different parameters? Do I need to register separate forces for each node? Or should the force be parameterizable, e.g., forceLink.strength takes a function that is evaluated for each link?
2. If the force is parameterizable, does that mean the parameters are re-evaluated when the array of nodes (or links) changes, or are the parameters evaluated every time the force is invoked? Is it worth trying to optimize the common case of constant-value forces?
3. If forces are parameterizable, why do we also need to specify the array of nodes to each force—couldn’t they just always use the array of nodes associated with the simulation, and you could define the strength as zero if you didn’t want the force to apply to those nodes?
4. If forces do always use the simulation’s array of nodes, should the simulation also keep track of the links? (Probably not, since I think links only need to be known by d3.forceLink, whereas multiple parties care about nodes?)

[mbostock]

1. Forces should be parameterized per node (or per link).
2. The parameters should be re-evaluated when the nodes (or links) or parameters change.
3. The forces should receive the nodes from the simulation (via the optional force.nodes method).
4. The simulation will not track links because these are only used by the link force.