https://topplegame.com/preflight.js

1(function () {
2  var ok = true;
3  try {
4    var c = document.createElement('canvas');
5    if (!c.getContext('webgl2')) ok = false;
6  } catch (e) {
7    ok = false;
8  }
9  if (typeof WebAssembly === 'undefined') ok = false;
10  if (!ok) {
11    document.documentElement.innerHTML =
12      '<head><meta charset="UTF-8"><title>Topple</title></head>' +
13      '<body style="margin:0;background:#161616;color:#eee;font:14px Manrope,-apple-system,system-ui,sans-serif;display:flex;align-items:center;justify-content:center;min-height:100vh;">' +
14      '<div style="text-align:center;padding:32px;max-width:480px;">' +
15      '<h1 style="font-size:18px;margin:0 0 12px;color:#eee;">Topple needs WebGL 2 and WebAssembly</h1>' +
16      '<p style="margin:0;color:#ccc;">Your browser doesn\'t support both. Please update to a recent version of Chrome, Firefox, Safari or Edge.</p>' +
17      '</div></body>';
18  }
19})();