regular expression to find ISBNs in text, URLs or microdata

isbn-regex.js

function matchISBNs(html) {
  // flatten string and find ISBN-looking things
  let isbns = html.replaceAll("\n", ' ').match("/(?=([0-9]|X|-){10,20})(97(8|9))?-?(0|1|8)([0-9]|-){8,14}([0-9]|X)/gi");

  if (!isbns || !isbns.length) 
    return;

  // remove dashes
  isbns = isbns.map((value) => value.replaceAll('-', ''));
  // throw out anything that isn't 10 or 13 characters
  isbns = isbns.filter((value, index, array) => (value.length == 10 || value.length == 13));
  // de-dupe
  isbns = isbns.filter((value, index, array) => array.indexOf(value) === index);
  
  return isbns;
}

let text = document.body.innerText;
let html = document.body.innerHTML;
//let html = document.getElementById('isbns').value;

// look in URLs
let hrefs = html.match(/href=(["'])(.*?)\1/gi);
// also in microdata
let itemids = html.match(/itemid=(["'])(.*?)\1/gi);

// combine URLs, microdata, and visible content
text += ' ' + hrefs + ' ' + itemids;

let isbns = matchISBNs(text);
// result: array of ISBNs without dashes

// demo: https://codepen.io/stephanieleary/full/XWLPWww
// bookmarklet: https://codepen.io/stephanieleary/full/bGPxGrW