Das,
if you create a business rule, it will run on the server side (In opposite of client script that runs on client side)
This following article explains the difference between the scripts into servicenow, it will help you to get a broader perspective of how and where to script in Servicenow : Differences Among Scripts - ServiceNow Wiki
To answer to your question, you can create a Before business rules.
Put the table name on which the Business rule should operate. Do not forget to check also the "advanced" checkbox (as you will need to script a little bit)
Under the filter condition, you can put something similar to this condition : State changes
Under advanced tab, You have to write your script. I only provide you the sample of the script that you can use :
(function executeRule(current, previous /*null when async*/) {
if (current.state == '3') { // make sure to put the value and not the label
current.u_status = "ValueOfTheStateOfYourChoice1";
}
if (current.state == '4') {
current.u_status = "ValueOfTheStateOfYourChoice2";
}
})(current, previous);
