Debugging an Error in Code

You're a software engineer on Sentry's event-ingestion team. This Node.js handler processes incoming error events from SDKs before they're stored, and it has started throwing in production under real traffic.

const counts = {};

function processEvent(event) {
  const payload = JSON.parse(event.body);

  const key = payload.projectId + ":" + payload.environment;
  counts[key]++;

  if (counts[key] > event.rateLimit) {
    sendResponse(429, "rate limited");
  }

  if (payload.environment == 0) {
    sendResponse(400, "invalid environment");
  }

  const severity = payload.level === "error" ? "high" : "low";
  storeEvent(payload, severity);
  sendResponse(200, "ok");
}

function sendResponse(status, message) {
  console.log(status, message);
}

function storeEvent(payload, severity) {
  console.log("stored", payload.id, severity);
}

Read through the handler and identify every issue you can find that would cause it to behave incorrectly or crash in production, including the specific error that would surface first. Explain what's wrong with each one and what you'd change.