Handle data updates from Shiny

dev/dev.Rmd

        ```
     1. Now, if nothing else, the `chart` object is accessible
        so others can use or extend it.
+1. Create an update method that takes new data and updates an existing chart.
+
+    Demo with `app.R`
+    
+    ```js
+    let el = document.getElementById('chart')
+    el.widget.update({x: ['A', 'B', 'C', 'D'], Frequency: [1, 2, 3, 4]})
+    ```
+    
+    Try with various values. You can increase the number of data points
+    but you can't add or change the series.
+
+1. Add a custom message handler that dependes on `HTMLWidgets.shinyMode`.
+
+    ```js
+    // after factory function
+    if (HTMLWidgets.shinyMode) {
+      Shiny.addCustomMessageHandler('frappeCharts:update', function({id, data}) {
+        let el = document.getElementById(id)
+        el.widget.update(data)
+      })
+    }
+    ```
+    
+    Restructure the app code so that the chart initializes with flat data (0.5).
+    Use `session$sendCustomMessage` to trigger the update.
+    
+    Note that the JS function above takes `id` and `data` using destructuring.
+    It's easy to write `function(id, data)` but this won't work because
+    the handler can only take one argument.
+    
+    Demo the app, now updates are fast!
+

dev/shiny/app.R

 )
 
 # Define server logic required to draw a histogram
-server <- function(input, output) {
+server <- function(input, output, session) {
+  initial_data <- data.frame(
+    x = LETTERS[seq_len(10)],
+    Frequency = rep(0.5, 10)
+  )
+
   data <- reactive({
     input$new_data
 
 
   output$chart <- frappeCharts::renderFrappeChart({
     frappeCharts::frappeChart(
-      data(),
+      initial_data,
       type = "bar",
       tooltipOptions = list(
         formatTooltipY = htmlwidgets::JS("d => Math.round(d * 100) + '%'")
       )
     )
   })
+
+  observe({
+    session$sendCustomMessage("frappeCharts:update", list(id = "chart", data = data()))
+  })
 }
 
 # Run the application

inst/htmlwidgets/frappeChart.js

 
       },
 
+      update: function(data) {
+        if (!chart) {
+          console.error("The chart has not yet been initialized.")
+        }
+        let chartData = prepareChartData(data)
+        chart.update(chartData)
+      },
+
       chart: () => chart
 
     };
   }
 });
+
+if (HTMLWidgets.shinyMode) {
+  Shiny.addCustomMessageHandler('frappeCharts:update', function({id, data}) {
+    let el = document.getElementById(id)
+    el.widget.update(data)
+  })
+}