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JavaScript SDK FAQ

Solutions to some commonly faced issues while using the RudderStack JavaScript SDK.

This guide contains the answers to some commonly-asked questions about setting up, using and troubleshooting the JavaScript SDK.

Should I disable ad blockers on my browser?

Yes, it is important to ensure that no ad blockers are running on your browser, as they restrict the JavaScript SDK script from executing and storing user information in the browser.

Can I load multiple instances of RudderStack JavaScript SDK?

No, it is not possible to load multiple instances of the JavaScript SDK, as it is bound to exceed the maximum stack call size and give you an error.

How can I verify if the SDK sends the data to the desired destinations?

To verify if the SDK is transmitting the events to the specified destinations, go to the Network tab of the JavaScript console in your browser.

Sample page call
Sample track call

If you cannot see any outbound requests, verify if you have installed and set up the JavaScript SDK correctly. Also, check if any adblockers are enabled on your browser.

What is the size limit on the event requests?

The JavaScript SDK exhibits the following behavior:

  • If the event size exceeds 32KB, the SDK logs an error message but forwards it to the RudderStack data plane (backend).
  • If you send the event using sendBeacon, the SDK batches the events with a size limit of 64KB on the entire batch payload. If a single event’s size exceeds 64KB, the browser might drop the event. Note that this is applicable for the JavaScript SDK v1.1.

Can I send the event data to specific destinations only?

Yes, you can send your event data only to the specific destinations by stopping the SDK from loading the other device mode integrations.

What is the “Reserved Keyword” error?

When using the JavaScript SDK, you may run into the following error:

Warning! : Reserved keyword used in traits -->  id with track call.

This is because one or more keys in your traits or properties object have the same value as a reserved keyword.

RudderStack reserves the following keywords as keys for a standard event payload, and you should avoid using these while naming your event traits and properties:


How can I differentiate between events sent from a mobile device or from a website using a laptop?

The events tracked via JavaScript SDK contain context.userAgent that contain information on the user agent of the device.

Questions? Contact us by email or on Slack