fullstorydev Fullstory Asynchronous Methods API
Implementation Files: This document covers core concepts. For code examples, see:
- SKILL-WEB.md — JavaScript/TypeScript (Browser)
- SKILL-MOBILE.md — Platform differences for iOS, Android, Flutter, React Native
Note: The
Asyncsuffix pattern is specific to the web/browser SDK. Mobile SDKs use different asynchronous mechanisms (completion handlers, delegates, listeners).
Overview
Fullstory's Browser API provides asynchronous versions of all methods by appending Async to the method name. These async methods return Promise-like objects that resolve when Fullstory has started and the action completes. This is essential for:
- Initialization Waiting: Wait for Fullstory to fully bootstrap before taking actions
- Session URL Retrieval: Get the session replay URL for logging, support tickets, etc.
- Error Handling: Know if an API call succeeded or failed
- Sequential Operations: Ensure operations complete in order
- Conditional Logic: Take action based on Fullstory state
Core Concepts
Sync vs Async Methods
| Method Type | Returns | Use When |
|---|---|---|
FS('methodName') |
undefined | Fire-and-forget, don't need result |
FS('methodNameAsync') |
Promise-like | Need result, error handling, or sequencing |
Promise-like Object
The object returned from async methods:
- Can be
awaited - Supports
.then()chaining - Important:
.catch()may not work in older browsers without Promise polyfill - May reject if Fullstory fails to initialize
Available Async Methods
Every FS method has an async variant:
| Sync Method | Async Method |
|---|---|
FS('setIdentity', {...}) |
FS('setIdentityAsync', {...}) |
FS('setProperties', {...}) |
FS('setPropertiesAsync', {...}) |
FS('trackEvent', {...}) |
FS('trackEventAsync', {...}) |
FS('getSession') |
FS('getSessionAsync') |
FS('shutdown') |
FS('shutdownAsync') |
FS('restart') |
FS('restartAsync') |
FS('log', {...}) |
FS('logAsync', {...}) |
FS('observe', {...}) |
FS('observeAsync', {...}) |
Return Values
| Method | Resolves With |
|---|---|
getSessionAsync |
Session URL string |
setIdentityAsync |
undefined (completion signal) |
setPropertiesAsync |
undefined |
trackEventAsync |
undefined |
shutdownAsync |
undefined |
restartAsync |
undefined |
observeAsync |
Observer object with .disconnect() |
Rejection Scenarios
The Promise may reject when:
- Malformed or missing configuration (no
_fs_org) - User on unsupported browser
- Error in
rec/settingsorrec/pagecalls - Organization over quota
- Fullstory script blocked by ad blocker (may not reliably reject)
When to Use Async vs Sync
Use Async When:
| Scenario | Why |
|---|---|
| Need session URL | Must wait for URL to be available |
| Error handling needed | Need to know if call failed |
| Sequential operations | Must ensure order of operations |
| Conditional logic | Need result to decide next action |
| Initialization checks | Need to know when FS is ready |
Use Sync (Fire-and-Forget) When:
| Scenario | Why |
|---|---|
| Simple event tracking | Don't need confirmation |
| Non-critical operations | Failure is acceptable |
| Performance critical paths | Don't want to add latency |
| Rapid-fire events | Queueing handles order |
| User-facing actions | Don't delay user experience |
Best Practices
1. Always Use Timeouts
// Prevent hanging if Fullstory is blocked
const result = await Promise.race([
FS('getSessionAsync'),
new Promise((_, reject) =>
setTimeout(() => reject(new Error('Timeout')), 5000)
)
]);
2. Don't Block Critical Paths
// BAD: App hangs if FS blocked
await FS('getSessionAsync');
renderApp();
// GOOD: App starts immediately
renderApp();
FS('getSessionAsync').then(url => enrichWithSession(url));
3. Use try/catch, Not .catch()
// GOOD: Works reliably
try {
const url = await FS('getSessionAsync');
} catch (error) {
// Handle error
}
// RISKY: .catch() may not work in older browsers
FS('getSessionAsync')
.then(url => {})
.catch(err => {}); // May fail silently
4. Handle Sequencing Correctly
// GOOD: Sequential operations
await FS('setIdentityAsync', { uid: user.id });
await FS('trackEventAsync', { name: 'Login' });
// BAD: Race condition
FS('setIdentityAsync', { uid: user.id });
FS('trackEventAsync', { name: 'Login' }); // May fire before identity!
Troubleshooting
Promise Never Resolves
| Cause | Solution |
|---|---|
| Fullstory blocked by ad blocker | Use timeout wrapper |
| Script failed to load | Check network tab |
| Network issues | Implement fallback behavior |
Rejection Errors
| Cause | Solution |
|---|---|
Missing _fs_org |
Check Fullstory setup |
| Unsupported browser | Verify browser compatibility |
| Over quota | Check Fullstory account |
.catch() Not Working
| Cause | Solution |
|---|---|
| No native Promise | Use async/await with try/catch |
| Promise-like limitations | Use .then() with error callback |
Key Takeaways for Agent
When helping developers with Async Methods:
Always emphasize:
- Use timeouts to prevent hanging
- Handle rejections gracefully
- Don't block critical paths on FS
- Use try/catch, not .catch()
Common mistakes to watch for:
- Blocking app startup on FS
- Missing error handling
- Using async when sync would work
- Race conditions between calls
- .catch() without polyfill check
Questions to ask developers:
- Do you need the result?
- Is this on a critical path?
- What should happen if FS fails?
- Is proper sequencing required?
Platform routing:
- Web (JavaScript/TypeScript) → See SKILL-WEB.md
- Mobile platforms → See SKILL-MOBILE.md for platform-specific patterns
Reference Links
- Asynchronous Methods: https://developer.fullstory.com/browser/asynchronous-methods/
- Get Session Details: https://developer.fullstory.com/browser/get-session-details/
- Callbacks and Delegates: https://developer.fullstory.com/browser/fullcapture/callbacks-and-delegates/