RUM JavaScript Agent gives a 'not iterable error' on Symbol.iterator

Bill_Emerson — Mon, 02 Feb 2026 10:04:38 GMT

Summary

Applications monitored by RUM generate JavaScript errors referring to Symbol.iterator when using RUM Agent 1.329 or higher. This is caused by the RUM Agent interacting with code that implements Array.prototype.find incorrectly in other JavaScript on the page.

Problem

Following the release of RUM JavaScript Agent 1.329, some customers have reported encountering JavaScript errors on pages utilising the Array.prototype.find() function. We are seeing errors arise when the front-end code using this function returns an invalid value, i.e. a value that does not satisfy the testing function.

Per the Mozilla documentation, this condition should return undefined not any other value. Returning an invalid value will cause the RUM JavaScript Agent to generate an error, which may affect the page loading.

Resolution

In order to resolve this issue, the other JavaScript code on the page must be modified so that it only returns valid values for this function.

As a temporary solution, you can update your RUM application to use version 1.327 of the RUM JavaScript agent. See how to Control the RUM JavaScript version.

What's next

This issue arises in version 1.329 because the RUM agent introduced functionality that utilises the Array.prototype.find method, which is only available in version 1.329 and above. Therefore, it relies on the correct implementation of the Array.prototype.find method if it is used by other JavaScript on the same page.

If this article did not help, please open a support ticket, mention that this article was used and provide the following in the ticket:

article RUM JavaScript Agent gives a 'not iterable error' on Symbol.iterator in Troubleshooting

RUM JavaScript Agent gives a 'not iterable error' on Symbol.iterator

Summary

Problem

Resolution

What's next