custom-elements/when-defined-reentry-crash.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>Check for crashes when a whenDefined promise resolving re-entries</title>
<meta name="author" href="mailto:xiaochengh@chromium.org">
<link rel="help" href="https://html.spec.whatwg.org/multipage/custom-elements.html#custom-elements-api">
<link rel="help" href="https://bugs.chromium.org/p/chromium/issues/detail?id=1366813">
<script>
class CustomElement extends HTMLElement {}

Object.prototype.__defineGetter__("then", main);

let depth = 0;
function main() {
  if (depth > 1) return;
  ++depth;
  customElements.whenDefined("custom-a"); // Causes re-entry of main()
  try { customElements.define("custom-a", CustomElement) } catch (e) {}
  customElements.whenDefined("custom-b");
  --depth;
}

main();
</script>

Test passes if it does not crash.