Which one fire first Java-script or Business Rule Running Order

JavaScript trigger and then trigger business rule.

Running Order

It’s possible you could have JavaScript and numerous business rules all running against one field, so the order things run can have a dramatic effect on the outcome.

1. Any system scripts are applied first.
2. Any logic in custom form scripts is applied.
3. Logic in business rules is applied.When there are multiple business rules, they are applied in the  order they were activated, from oldest to newest.