Current documentation on the Javascript objects available in the duktape runtime does not contain reference to the btoa() and atob() functions.

Page to update:

https://www.zabbix.com/documentation/5.0/manual/config/items/preprocessing/javascript/javascript_objects

Some reference to these methods can be found in the javascript preprocessing documentation for version 4.4 at: 

https://www.zabbix.com/documentation/4.4/manual/appendix/preprocessing/javascript

and the 5.0 documentation at:

https://www.zabbix.com/documentation/5.0/manual/config/items/preprocessing/javascript

But since their availability is not limited to preprocessing I propose they are documented in the javascript_objects section which is referenced by both the webhook and perprocessing documentation.