Why .js file created in doctypes what it does? what is use of that .js file?

[Vegeshna_Satyanaraya]

why .js file created in doctypes what it does? what is use of that .js file?

[rmehta]

You can add triggers for form events. See example: https://github.com/frappe/frappe/blob/develop/frappe/core/doctype/event/event.js