Extract CSS classes out of HTML code

html-classes-to-css.js

/*
* Use this script to extract CSS classes out of HTML code. 
* Replace the test HTML code on line 8-9 with your HTML code.
* Run `node html-classes-to-css.js` in your terminal and a CSS file will be generated.
*/

const fs = require("fs");

var html =
  `<div id="1432" class="test class-test another-class"><p class="bold text-small something"></p></div>`;
extractClasses(html);

function extractClasses(html) {
  var classNameSet = new Set();

  var classesIndex = html.indexOf('class="');

  while (classesIndex > -1) {
    var classesStartIndex = classesIndex + 7;
    html = html.substring(classesStartIndex);
    var classesEndIndex = html.indexOf('"');
    var currentClassNames = html.substring(0, classesEndIndex).split(" ");
    //console.log(html.substring(0, classesEndIndex));

    currentClassNames.forEach((className) => {
      classNameSet.add(className);
    });

    classesIndex = html.indexOf('class="');
  }

  console.log(classNameSet);

  var classArray = Array.from(classNameSet);
  var template = "";
  classArray.forEach((className) => {
    template += `.${className} { }\n\n`;
  });

  fs.writeFile("template.css", template, (error) => {
    if (error) {
      console.error(error);
      return;
    }
  });
}