How to Fix Performance Api Error in Svelte

The performance api error in Svelte can be frustrating, especially when it appears without an obvious cause. Let's break down exactly what's happening and how to resolve it quickly.

Why This Happens

The Performance API error appears when your Svelte code calls performance.mark(), performance.measure(), or similar methods in an environment where the performance global doesn't exist. This commonly happens during server-side rendering where browser APIs are unavailable.

The Solution

<!-- In a Svelte component, use onMount -->
<script>
import {{ onMount }} from "svelte";

onMount(() => {{
  performance.mark("component-ready");
  return () => {{
    // Cleanup: measure on unmount
    if (performance.getEntriesByName("component-ready").length) {{
      performance.measure("component-lifetime", "component-ready");
    }}
  }};
}});
</script>

Use onMount to ensure Performance API calls run client-side only. The returned cleanup function handles measurement on unmount.

Additional Considerations

• The Performance API is browser-only — Node.js provides a separate perf_hooks module with a different import pattern
• Some older browsers have incomplete implementations of the Performance Timeline API
• Always wrap performance instrumentation in try-catch blocks so measurement failures never break your application
• Consider using the PerformanceObserver API for more robust measurement collection

Environment Detection Pattern

When writing isomorphic Svelte code, create a utility function that safely wraps Performance API calls:

const safeMark = (name) => {
  if (typeof performance !== "undefined" && performance.mark) {
    performance.mark(name);
  }
};

[Bugsly](https://bugsly.dev) can track Performance API errors across your Svelte deployment and help you identify exactly which environments and code paths trigger failures.