code: function serializeState(){
        var data = model.data,
            scale = model.scale,
            translate = model.translate;
        model.state = {
          nodes: data.nodes.map(function(node){
            return {
              type: node.type,
              property: node.property,
              fixed: node.fixed,
  
              // Keep size of JSON small, so it fits in a URL.
              x: Math.round(node.x),
              y: Math.round(node.y)
            };
          }),
          links: data.links.map(function(link){
            // Replaced link object references with indices for serialization.
            return {
              source: link.source.index,
              target: link.target.index
            };
          }),
          scale: scale,
          translate: translate
        };
      }
docs: Sets model.state to expose the serialized state.