I have three custom fields for one built-in object say ObjA. I would like to fiell Custom Field C when end-user changes values of custom field A and/or B in the edit form of ObjA, before the object is saved.

I will call javascript function to do that.

What is the easiest way to do this? I am new to Salesforce. I expect something like this: create a javascript file with my functions, associate it with the object edit form (maybe some customization to the object/form).

Thanks,

I have three custom fields for one built-in object say ObjA. I would like to fiell Custom Field C when end-user changes values of custom field A and/or B in the edit form of ObjA, before the object is saved.

I will call javascript function to do that.

What is the easiest way to do this? I am new to Salesforce. I expect something like this: create a javascript file with my functions, associate it with the object edit form (maybe some customization to the object/form).

Thanks,