Generate the required blank duplex page

import assert from 'node:assert/strict';
import {createRequire} from 'node:module';
import {pathToFileURL} from 'node:url';
const htmlEscape=s=>String(s).replace(/&/g,'&amp;').replace(/</g,'&lt;').replace(/>/g,'&gt;').replace(/"/g,'&quot;');
async function withPage(action,options={}){
  const require=createRequire(import.meta.url);const {chromium}=require('playwright');
  const browser=await chromium.launch({headless:true});
  try{const context=await browser.newContext(options);const page=await context.newPage();
    const requests=[];await page.route('**/*',route=>{requests.push(route.request().url());return route.abort();});
    return await action(page,context,requests);
  }finally{await browser.close();}
}
async function pdfObservation(html){
  const bytes=await withPage(async page=>{await page.setContent(html);return page.pdf({preferCSSPageSize:true,printBackground:true});});
  const require=createRequire(import.meta.url);
  const {getDocument}=await import(pathToFileURL(require.resolve('pdfjs-dist/legacy/build/pdf.mjs')).href);
  const loadingTask=getDocument({data:Uint8Array.from(bytes),useSystemFonts:true,disableFontFace:true});
  try{const document=await loadingTask.promise;const pages=[];for(let n=1;n<=document.numPages;n++){
    const page=await document.getPage(n);const content=await page.getTextContent();
    pages.push(content.items.filter(x=>typeof x.str==='string'&&x.str).map(x=>({text:x.str,x:x.transform[4],y:x.transform[5]})));
  }return {pageCount:document.numPages,pages};}finally{await loadingTask.destroy();}
}
const printStyle='<style>@page{size:100mm 100mm;margin:10mm}body{margin:0;font:10px Arial}p{margin:0}</style>';

const run=async function run(i,corrected=true){
    if(typeof i.frontRequired!=='boolean'||![2,3].includes(i.priorPages))return {held:true};
    const blank=corrected&&i.frontRequired&&i.priorPages%2===1?'<section class="prior"></section>':'';
    const html=printStyle+'<style>.prior{height:80mm;break-after:page}.next{break-before:page}</style>'+Array.from({length:i.priorPages},(_,n)=>'<section class="prior">PRIOR'+(n+1)+'</section>').join('')+blank+'<section class="next">NEWSECTION</section>';
    const out=await pdfObservation(html);return {newSectionPage:out.pages.findIndex(p=>p.some(x=>x.text==='NEWSECTION'))+1,blankPages:out.pages.map((p,n)=>p.length?null:n+1).filter(n=>n!==null),pageCount:out.pageCount};
  };
const cases=[{"input":{"priorPages":3,"frontRequired":true},"corrected":false,"expected":{"newSectionPage":4,"blankPages":[],"pageCount":4}},{"input":{"priorPages":3,"frontRequired":true},"corrected":true,"expected":{"newSectionPage":5,"blankPages":[4],"pageCount":5}},{"input":{"priorPages":2,"frontRequired":true},"corrected":true,"expected":{"newSectionPage":3,"blankPages":[],"pageCount":3}},{"input":{"priorPages":3,"frontRequired":null},"corrected":true,"expected":{"held":true}}];
for(const test of cases){const actual=await run(test.input,test.corrected);assert.deepEqual(actual,test.expected);console.log(actual);}