dupIds

gistfile1.txt

const ids = Array.from(document.querySelectorAll('[id]'))
  .map(v => v.id)
  .reduce((acc, v) => {
    acc[v] = (acc[v] || 0) + 1;
    return acc
  }, {});

console.log(ids);

// To get a list of duplicate IDs:
const duplicateIds = Object.entries(ids)
  .filter(([key, value]) => value > 1)
  .map(([key, value]) => key);

console.log(duplicateIds);