Different event used in query report(script report)

I am creating a query report where I have two field like cust_code and cust_name.
when I select cust_code it will auto select the respective cust_name (name and code are fetch from database) and also does the vice versa.

I did it by in cust_code

“on_change”: function() {

I did it by in cust_name

“on_change”: function() {

but issued is that when I changed value of one it will called on_change event of other.
I just found that there are only two method used in query report like “on_load” and “on_change”.
I had also tried with “on_update”, “on_click” but none are affected in operation.
If you know any other event except this or any other way then please let me know.
Thanks in advance