This is a simple real world example.

There was a customer need to set a field values based on value of another field on the opportunity screen. The screens had been customized. The oppo_forecast and oppo_certainty fields were removed from the opportunitystatusbox and oppo_certainty was added to the opportunitydetailbox screen along with a new field called oppo_forecastcategory. Oppo_forecastcategory was a Selection list. Its values were either 'None', 'A' 'B', 'C', 'D.

If the changes the drop down field Forecast Category to "˜B', the Certainty value needs to set to 40.

This can be expressed as an onChange rule

The code used was:

switch (this.value) {
case 'A' :
oppo_certainty.value = '20';
break;
case 'B' :
oppo_certainty.value = '40';
break;
case 'C' :
oppo_certainty.value = '60';
break;
case 'D' :
oppo_certainty.value = '80';
break;
default :
oppo_certainty.value = '5';
}