code: function resolveNodeSkel(index, nodeName) {
      var idx = +graph.nameToIndex[nodeName];
      argh = [idx, +index]
      if(Number.isNaN(idx)) {
        throw "Unable to get index for node '" + nodeName + "'. (Is the node name misspelled?)";
      }
      if(index !== undefined && idx > +index) {
        throw "Unable to get index for node '" + nodeName + "'. (Are the nodes out of order?)";
      }
      if(index !== undefined && idx == +index) {
        throw "Unable to get index for node '" + nodeName + "'. (Is the node trying to reference itself?)";
      }
      return (dataContext) => dataContext.values[idx];
    }
docs: Helper function to lookup a node