d3_to_png.js

var fs = require("fs");
var d3 = require("d3");
var jsdom = require("jsdom/lib/old-api");
var svg2png = require("svg2png")

var width = 400;
var height = 300;

jsdom.env({
    html:'',
    features:{ QuerySelector:true }, // you need query selector for d3 to work
    done:function(errors, window){
        window.d3 = d3.select(window.document); //get d3 into the dom

        var container = window.d3.select("body").append("div").attr("class", "container");
        
        var svg = container.append("svg")
            .attr('xmlns', 'http://www.w3.org/2000/svg')
            .attr("width", width)
            .attr("height", height);
        
        // set background color of SVG to white, otherwise it defaults to transparent
        var bg = svg.append("rect")
            .attr("width", "100%")
            .attr("height", "100%")
            .attr("fill", "#ffffff");

        var circle = svg.append("circle")
            .attr("cx", 30)
            .attr("cy", 30)
            .attr("r", 20)
            .attr("stroke", "#cc0000")
            .attr("stroke-width", 2)
            ;
        
        var data = container.html();

        fs.writeFileSync("output.svg", data)
        
        svg2png(data)
            .then(buffer => fs.writeFile("output.png", buffer))
            .catch(e => console.error(e));
    }
});