Steps to reproduce:

1. Create item.
2. Item type - script.
3. Item type of information - text.
4. In script field add - 

   return '🥕';

1. Navigate to Preprocessing tab.
2. Add new step - JavaScript.
3. In parameters add - return value + value;
4. Press test button.
5. Check in - Get value from host.
6. Press - Get value and test button.

Result:

Error message - could not convert return value to utf8

Expected:
No errors.