insert variable scoping sections to insert functions + source functions

Author: sade-wusi

src/connections/functions/insert-functions.md

@@ -111,6 +111,12 @@ To ensure the Destination processes an event payload modified by the function, r
 > 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, make sure to declare them in the function handler rather than globally in your Function. This prevents you leaking the settings values across other function instances.
+
+The handler for Insert functions is event-specific, for example, `onTrack()`, `onIdentify()`, etc.
+
 ### Errors and error handling
 
 Segment considers a function's execution successful if it finishes without error. You can `throw` an error to create a failure on purpose. Use these errors to validate event data before processing it to ensure the function works as expected.

src/connections/functions/source-functions.md

@@ -261,6 +261,12 @@ The `Segment.set()` method accepts an object with the following fields:
 > warning ""
 > When you use the `set()` method, you won't see events in the Source Debugger. Segment only sends events to connected warehouses.
 
+### Variable scoping
+
+Declare settings variables 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 Source functions is `onRequest()`.
+
 ### Runtime and dependencies
 
 {% include content/functions/runtime.md %}