css/css-text/text-autospace/text-autospace-dynamic-text-001.html

<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-text-4/#text-autospace-property">
<link rel="help" href="text-autospace-dynamic-text-001-ref.html">
<div id="target">国国</div>
<script>
const target_text = document.getElementById('target').firstChild;
for (const ch of 'AA国国AA国国') {
  document.body.offsetTop;  // Force layout.
  target_text.appendData(ch);
}
</script>