https://www.idahoreportcard.org/js/bootstrapModalErrorGuard.js

1// Defensive guard for rare Bootstrap modal race conditions in SPA navigation.
2// In Blazor, the DOM can be replaced while a Bootstrap modal transition callback is still running.
3// This can surface as "Cannot read properties of null (reading 'style')" from modal.js/_hideModal.
4
5(function () {
6  function looksLikeBootstrapModalHideNullStyle(err) {
7    const msg = (err && (err.message || err.toString())) || '';
8    if (!msg) return false;
9
10    // Match common variants across browsers/bundles.
11    return (
12      msg.includes("Cannot read properties of null") && msg.includes("style") && (msg.includes("modal") || msg.includes("_hideModal"))
13    ) || (
14      msg.includes("Cannot read property 'style' of null") && (msg.includes("modal") || msg.includes("_hideModal"))
15    );
16  }
17
18  function safeCleanupArtifacts() {
19    try {
20      if (window.bootstrapModalCleanup && typeof window.bootstrapModalCleanup.cleanupModalArtifacts === 'function') {
21        window.bootstrapModalCleanup.cleanupModalArtifacts();
22      }
23    } catch {
24      // ignore
25    }
26  }
27
28  window.addEventListener('error', (e) => {
29    const err = e?.error || e;
30    if (!looksLikeBootstrapModalHideNullStyle(err)) {
31      return;
32    }
33
34    // Prevent the error from surfacing as an unhandled exception.
35    try { e.preventDefault?.(); } catch { /* ignore */ }
36
37    // Best-effort cleanup so the UI isn't left stuck.
38    safeCleanupArtifacts();
39  });
40
41  window.addEventListener('unhandledrejection', (e) => {
42    const err = e?.reason;
43    if (!looksLikeBootstrapModalHideNullStyle(err)) {
44      return;
45    }
46
47    try { e.preventDefault?.(); } catch { /* ignore */ }
48    safeCleanupArtifacts();
49  });
50})();