Estaba haciendo referencia a algunas variables y funciones que no estaban dentro del alcance de su función...

 library(jsonlite) library(networkD3) library(htmlwidgets) URL <- paste0('https://cdn.rawgit.com/christophergandrud/networkD3/', 'master/JSONdata/energy.json') energy <- jsonlite::fromJSON(URL) p <- sankeyNetwork(Links = energy$links, Nodes = energy$nodes, Source = 'source', Target = 'target', Value = 'value', NodeID = 'name', units = 'TWh', fontSize = 12, nodeWidth = 30) htmlwidgets::onRender( p, ' function(el,x){ // map the variables you are trying to use below var options = x.options; var sankey = this.sankey; // replicate the private functions from the renderValue function that you call below var color = eval(options.colourScale); var color_node = function color_node(d){ if (d.group){ return color(d.group.replace(/ .*/, "")); } else { return "#cccccc"; } } var formatNumber = d3.format(",.0f"), format = function(d) { if (typeof d === "string") return d; return formatNumber(d); } //node variable var node=d3.select(el).select("svg").selectAll(".node"); //remove node node.selectAll("rect") .remove(); // add circles instead node .append("circle") .attr("cx",sankey.nodeWidth()/2) .attr("cy",function(d){ return d.dy/2; }) .attr("r",function(d){ return Math.sqrt(d.dy);}) .style("fill", function(d) { return d.color = color_node(d); }) .style("stroke", function(d) { return d3.rgb(d.color).darker(2); }) .style("opacity", 0.9) .style("cursor", "move") .append("title") .append("foreignObject") .append("xhtml:body") .html(function(d) { return "<pre>" + d.name + "<br>" + format(d.value) + " " + options.units + "</pre>"; }) ; } ' )