shiny json

graph.js

<style>

.node {
  stroke: #fff;
  stroke-width: 1.5px;
}

.link {
  stroke: #999;
  stroke-opacity: .6;
}

</style>

<script src="http://d3js.org/d3.v2.js"></script>
<script type="text/javascript">var networkOutputBinding = new Shiny.OutputBinding();
  $.extend(networkOutputBinding, {
    find: function(scope) {
      return $(scope).find('.shiny-network-output');
    },
    renderValue: function(el, data) {
      
      //format nodes object
      var nodes = new Array();
      for (var i = 0; i < data.names.length; i++){
        nodes.push({"name": data.names[i]})
      }


      var width = 800;
      var height = 600;
    
      var lin = data.links
      var force = d3.layout.force()
        .nodes(nodes)
        .links(lin)
        .charge(-120)
        .linkDistance(30)        
        .size([width, height])
        .start();
      
      //remove the old graph
      var svg = d3.select(el).select("svg");      
      svg.remove();
      
      $(el).html("");
      
      //append a new one
      svg = d3.select(el).append("svg");
      
      svg.attr("width", width)
        .attr("height", height);
    
      var link = svg.selectAll("line.link")
          .data(lin)
        .enter().append("line")
          .attr("class", "link")
          .style("stroke-width", function(d) { return Math.sqrt(d.value); });
    
      var node = svg.selectAll("circle.node")
          .data(nodes)
        .enter().append("circle")
          .attr("class", "node")
          .attr("r", 5)
          //.style("fill", function(d) { return color(d.group); })
          .call(force.drag);
      node.append("title")
        .text(function(d) { return d.name; });
        
        
      force.on("tick", function() {
        link.attr("x1", function(d) { return d.source.x; })
            .attr("y1", function(d) { return d.source.y; })
            .attr("x2", function(d) { return d.target.x; })
            .attr("y2", function(d) { return d.target.y; });
    
        node.attr("cx", function(d) { return d.x; })
            .attr("cy", function(d) { return d.y; });
      });
      
    }
  });
  Shiny.outputBindings.register(networkOutputBinding, 'trestletech.networkbinding');
  
  </script>

server.r

#almost entirely based on the 02_text and 03_mpg examples provided by RStudio Shiny
#all credit belongs to them


if (!require(PerformanceAnalytics)) {
  stop("This app requires the PerformanceAnalytics package. To install it, run 'install.packages(\"PerformanceAnalytics\")'.\n")
}

if (!require(quantmod)) {
  stop("This app requires the quantmod package. To install it, run 'install.packages(\"quantmod\")'.\n")
}

# Download data for a stock, if needed
require_symbol <- function(symbol) {
  if (!exists(symbol))
    getSymbols(symbol, src="FRED")
    #getSymbols(symbol, from = "1900-01-01")
}

library(shiny)

# Define server logic required to summarize and view the selected dataset
shinyServer(function(input, output) {
  make_chart <- function(symbol="SP500") {
    # get price data if does not exist
    require_symbol(symbol)

    #would hope not to recalculate each time but for now will leave messy
    price.monthly <- to.monthly(get(symbol))[,4]
    ret.monthly <- ROC(price.monthly, type="discrete", n=1)

    #calculate system returns
    systemRet <- merge(
      ifelse(lag(price.monthly > runMean(price.monthly, n=input$nmonths), k=1), 1, 0) * ret.monthly,
      ret.monthly)
    colnames(systemRet) <- c(paste(input$nmonths,"MASys",sep=""), symbol)

    charts.PerformanceSummary(systemRet, ylog=TRUE)
  }

  make_table <- function(symbol="SP500") {
    # get price data if does not exist
    require_symbol(symbol)

    #would hope not to recalculate each time but for now will leave messy
    price.monthly <- to.monthly(get(symbol))[,4]
    ret.monthly <- ROC(price.monthly, type="discrete", n=1)

    #calculate system returns
    systemRet <- merge(
      ifelse(lag(price.monthly > runMean(price.monthly, n=input$nmonths), k=1), 1, 0) * ret.monthly,
      ret.monthly)
    colnames(systemRet) <- c(paste(input$nmonths,"MASys",sep=""), symbol)

    table.Stats(systemRet)
  }
  
 # Generate a plot of the system and buy/hold benchmark given nmonths parameter
  # include outliers if requested
  output$systemPlot <- reactivePlot(function() {
    make_chart()
  })

  # Generate a summary stats table of the dataset
  output$json <- reactivePrint(function() {
    make_table()
  })

})

ui.r

#almost entirely based on the 02_text and 03_mpg examples provided by RStudio Shiny
#all credit belongs to them

library(shiny)

# Define UI for dataset viewer application
shinyUI(pageWithSidebar(
  
  # Application title
  headerPanel("Shiny Moving Average Parameter Test"),
  
  # Sidebar with controls to select a dataset and specify the number
  # of observations to view
  sidebarPanel(
    numericInput("nmonths", "Number of months for moving average:", 10)
  ),
  
  # Show a summary of the dataset and an HTML table with the requested
  # number of observations
  mainPanel(
    plotOutput("systemPlot"),
    verbatimTextOutput("json")
  )
))

I have download this sample . but when I run with " runApp" command . an error is occurred
object 'SP500' not found. can you explain me relationship of JS and Shiny in this sample?