preproc.js

const fs = require('fs')
const jsdom = require("jsdom")
const path = require('path')
const slideDir = "slides"

// Embed SVGs into file, allows the definition of fragment animation
module.exports = (markdown, options) => {
  return new Promise((resolve, reject) => {

      //Matching an entire object tag
      let re = /<object.*?data="(.*?)".*?>([- <>"'=a-zA-z0-9\n\/]*)<\/object>/gm
      //let paramRe = /<param class="".*?data="".*?\/>/gm;

      //Matching an opening of SVG tag
      let svgx = /<svg/gm

      /**
       * Replace an <object> with <svg> from the object's path
       * @param match regex match object
       * @param svg_path
       * @param obj_body
       * @returns svg string
       */
      function objReplace(match, svg_path, obj_body){
        //console.log("Replacing something " + svg_path + " " + obj_body);
        let svgRaw = fs.readFileSync(path.join(slideDir,svg_path), 'utf8')
        let svgStr = svgRaw.slice(svgRaw.search(svgx))
        let svgDom = new jsdom.JSDOM(svgStr)
        let svgDoc = svgDom.window.document
        let svgElem = svgDom.window.document.body.children[0]

        let objDom = new jsdom.JSDOM(match);
        let objElem = objDom.window.document.body.children[0]

        // Transfer style attribute from object to svg
        let styleAttribute = objElem.getAttribute("style")
        if(styleAttribute && styleAttribute.length > 0){
            svgElem.setAttribute("style", styleAttribute)
        }

        for(let i in objElem.children){
            let child = objElem.children[i]
            if(child.tagName === "PARAM")
            {
                let idAttr = child.getAttribute("id")
                let classAttr = child.getAttribute("class")
                let indexAttr = child.getAttribute("data-fragment-index")
                //console.log(`Attr: ${idAttr} ${classAttr} ${indexAttr}`);

                if(idAttr){
                    let graphicsElem = svgDoc.getElementById(idAttr)
                    if(graphicsElem){
                        if(classAttr)
                            graphicsElem.setAttribute("class", classAttr)

                        if(indexAttr)
                            graphicsElem.setAttribute("data-fragment-index", indexAttr)
                    }
                }
            }

        }

        let processedSvgStr = svgDom.window.document.body.innerHTML

        return processedSvgStr

      }
      const processedMd = markdown.replace(re, objReplace)

    resolve(processedMd)

  })
}