The business rule was introduced to provide a no code solution to drive both client side and server side logic. Business rule is efficient to replace the JavaScript so that the coding efforts are reduced to a great extent.

Now the question comes in mind, if we both business rule and JavaScript executing for the same functionality or having a common output then which of them will trigger first.

In terms of CRM 365, basically be it be a JavaScript or Business Rule, both gets processed only as JavaScript file. Eventually, JavaScript files will get loaded in lesser time compared to Business Rule as it doesn’t require any conversion to JavaScript format.

Thus as a conclusion, the JavaScript will always load and execute before the business rule.

For understanding more about the business rules click here.