Merge pull request segmentio#7512 from sade-wusi/patch-7

Update destination functions - including variable scoping [DOC-1065]

Author: sade-wusi

src/connections/functions/destination-functions.md

@@ -79,6 +79,12 @@ To change which event type the handler listens to, you can rename it to the name
 > info ""
 > Functions' runtime includes a `fetch()` polyfill using a `node-fetch` package. Check out the [node-fetch documentation](https://www.npmjs.com/package/node-fetch){:target="_blank"} for usage examples.
 
+### Variable scoping 
+
+When declaring settings variables, declare them in the function handler rather than globally in your function. This prevents you from leaking the settings values across other function instances. 
+
+The handler for destination functions is event-specific. For example, you might have an `onTrack()`or `onIdentify()` function handler.
+
 ### Errors and error handling
 
 {% include content/functions/errors-and-error-handling.md %}