Grab existing visjs DOM object on html page, change visjs options. http://visjs.org/ , R htmlwidgets

visjs-grab.js

// Grab existing  visjs DOM object on html page, change options
// knb 2018-12-08
// http://visjs.org/    Visualisation Library

// get similar id e.g. by inspecting HTML page source code that was generated by R htmlwidgets package
var = "htmlwidget-4210fec5d0f413c28b94"; 
var el = document.getElementById("graph" + widget);

var network = el.chart;

el.nodes.length; // should print a single int
el.chart.setOptions({
        nodes: {
            shape: 'dot',
            size: 30,
            font: {
                size: 13
            },
            borderWidth: 2,
            shadow:true
        },
        edges: {
            width: 2,
            shadow:true
        }
});