function detectTraceback(errorText) {
  if (!errorText) return false;
  return /^\s{4}at /m.test(errorText);
}

const encodedTraceback =
  "Error: ReferenceError: a is not defined%0A    at eval (eval at <anonymous> (_console1778948572008_0:1:46), <anonymous>:1:1)%0A    at _console1778948572008_0:1:46%0A    at _console1778948572008_0:1:60%0A    at exports.evalCode (<runtime>:15347:63)%0A    at exports.run (<runtime>:20876:41)%0A";

console.log("Encoded match:", detectTraceback(encodedTraceback));

const decodedTraceback = decodeURIComponent(encodedTraceback);
console.log("Decoded match:", detectTraceback(decodedTraceback));