Frappe.ui.form.on { ajax}

Does customer.js frappe.ui.form.on only execute once when the page is not refresh? What i means is [the scenario is like this: in customer list, i click on customer A , then it will enter to the specific customer page, which also execute the customer.js, i back again, then i click on customer B , then it will execute the customer.js as well. However, when i click on customer A on the customer list second time, the customer.js is NOT execute anymore by using frappe.ui.form.on , i place ajax inside frappe.ui.form.on. Could anyone please help me ?