There is no counterpart to the pathfinder panel in ExtendScript. The closest there is are menu commands for the pathfinder effect (Effect > Pathfinder). These are applied to a selected group, so the paths need selecting and grouping before, and apply effects, so they need expanding after. E.g.
app.executeMenuCommand("group");
app.executeMenuCommand("Live Pathfinder Add");
app.executeMenuCommand("expandStyle");
app.executeMenuCommand("ungroup");
// Add Live Pathfinder Add
// Intersect Live Pathfinder Intersect
// Exclude Live Pathfinder Exclude
// Subtract Live Pathfinder Subtract
// Minus Back Live Pathfinder Minus Back
// Divide Live Pathfinder Divide
// Trim Live Pathfinder Trim
// Merge Live Pathfinder Merge
// Crop Live Pathfinder Crop
// Outline Live Pathfinder Outline
// Hard Mix Live Pathfinder Hard Mix
// Soft Mix Live Pathfinder Soft Mix
// Trap Live Pathfinder Trap