If you're expecting those keys to be defined in the first element of the "items" array like the example code, you can do this:

If responseData.items.%GetTypeOf(0) = "object" {
  Set pResponse.COMPortalURL = responseData.items.%Get(0).portalUrl
}

This assumes that "items" will always be present and be an array. It checks if the first element of "items" is a nested object, and then sets the target object property to the value of portalUrl in the nested "items" object. You don't need to check if portalUrl is defined since referencing an unassigned key in a %DynamicObject will return the empty string instead of <UNDEFINED>.

The next versions of the three extensions (vscode-objectscript, Server Manager and Language Server) will attempt to close their web sessions when VS Code shuts down. This should help avoid sessions stacking up if you restart VS Code often.