Switch out the current R shiny htmlwidget data for updated data

Recently, I encountered an issue with a htmlwidget in one of my R shiny applications. Each time the widget render function was called multiple times, it failed to replace the existing data with new data. This bug caused the old data to linger and the new data to be appended on top of it.

To demonstrate this problem, I created a reproducible example. By clicking on the 'ui2' button, the application transitions to another ui. Then, upon clicking the 'reset' button from that ui, it returns to the default ui where you can observe two histograms within the same container instead of just one. This anomaly occurs because I am struggling to replace the old data with new data in my htmlwidget.

Reproducible Shiny App:

#library(devtools)
#install_github('radhikesh/d3Viz')
library(shiny)
library(d3Viz)

# Rest of the server code...

d3Histogram.js code

// JavaScript code for the d3Histogram widget goes here
//....

I believe the root cause lies in replacing the old data with new data in the JavaScript binding, but my knowledge of JavaScript is limited, making it challenging to address this issue. Any assistance or guidance would be greatly appreciated.

Thank you,

Radhikesh

Answer №1

Having encountered a similar problem, I found a solution that involved clearing out the existing child nodes of the container before adding new ones.

To achieve this, consider implementing the following while loop at the start of the renderValue function:

while (document.getElementById(el.id).hasChildNodes()) {
    document.getElementById(el.id).removeChild(document.getElementById(el.id).lastChild);
}

Answer №2

When your 'htmlwidget' sends messages to the browser with data, it updates the DOM and runs the JavaScript again. While the data is used to create an SVG, the data itself still exists separately from the SVG. The problem arises when the old SVG retains its previous state.

In your code, there is no built-in method to remove the existing plot or SVG when new data is sent in your JS file. One solution I often use is:

this.element.innerHTML = '';

Here, `this` refers to the current widget scope and `element` corresponds to `el` in the widget. By setting `innerHTML = ''`, you are essentially clearing the existing DOM element to allow for a new image to be appended by your script.

A good practice for your widget would be to include this kind of cleanup step before any new drawing operations. More intricate widgets may use transitions in d3 to move from the old state to the new one, but this typically requires custom bindings.

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