How to Fix Generator Error in Svelte

Nothing disrupts a coding session quite like an unexpected Generator Error in Svelte. Here's how to diagnose and fix it.

Root Cause

Generator errors in Svelte happen when using function* or async function* incorrectly — missing the asterisk, forgetting yield, or trying to consume generator objects where arrays are expected.

Step-by-Step Fix

The key is to collect async generator values into a reactive array for Svelte rendering updates:

<script>
  let values = [];

  async function* counter(max) {
    for (let i = 0; i < max; i++) {
      await new Promise(r => setTimeout(r, 300));
      yield i;
    }
  }

  async function start() {
    for await (const val of counter(10)) {
      values = [...values, val];
    }
  }
  start();
</script>

{#each values as v}<span>{v} </span>{/each}

Common Pitfall

Before diving into code changes, double-check your environment variables and Svelte version. Version mismatches between local and deployed environments are a frequent source of this error. While you're at it, check if your logging captures enough context around this error to speed up debugging next time.

Validate the Solution

Verify by triggering the same action that caused the original error. In Svelte, you can also enable verbose logging temporarily to confirm the fix is applied correctly. Once verified, remove or reduce the logging level to keep your logs clean in production.

Stay Ahead of Errors

Tools like [Bugsly](https://bugsly.dev) can catch these Svelte errors in real time, giving you stack traces and context to fix issues faster.