Fix Scheduler postTask Error in React

Scheduler postTask Errors in React

The Scheduler API (scheduler.postTask()) is a newer browser API for prioritized task scheduling. Errors occur when code assumes its availability across all environments.

Why It Errors

• Browser doesn't support the Scheduler API (still experimental)
• Server-side rendering where scheduler is undefined
• Older browser versions in your user base
• Test environments lacking the API

Fix with Feature Detection

// Bad: assuming scheduler API exists
scheduler.postTask(() => processQueue(), {
  priority: "background"
}); // TypeError: scheduler is not defined

// Good: polyfill + detection
const schedule = (fn, priority = "background") => {
  if (globalThis.scheduler?.postTask) {
    return scheduler.postTask(fn, { priority });
  }
  return Promise.resolve().then(fn);
};

Priority Levels Explained

• `user-blocking`: Highest priority, for input responses
• `user-visible`: Default, for visible UI updates
• `background`: Lowest, for non-urgent work

Compatibility Notes

1. Check [caniuse.com](https://caniuse.com) for current browser support
2. Always provide a fallback — this API is not universally available
3. Use `scheduler.yield()` for long tasks if supported
4. Consider libraries like `main-thread-scheduling` for broader compatibility

Bugsly Reports API Availability Issues

[Bugsly](https://bugsly.io) shows you which browsers and environments trigger Scheduler API errors, helping you decide whether to polyfill or drop the feature — backed by real user data.