Expense Claim Approval Status Additional

I was exploring on the codes in expense claim i just to ask if can i add a approval status.
And i would like to ask where does these codes connects to the expense_claim.js??

def set_status(self):
	self.status = {
		"0": "Draft",
		"1": "Submitted",
		"2": "Cancelled"
	}[cstr(self.docstatus or 0)]

	paid_amount = flt(self.total_amount_reimbursed) + flt(self.total_advance_amount)
	precision = self.precision("total_sanctioned_amount")
	if (self.is_paid or (flt(self.total_sanctioned_amount) > 0
		and flt(self.total_sanctioned_amount, precision) ==  flt(paid_amount, precision))) \
		and self.docstatus == 1 and self.approval_status == 'Approved':
			self.status = "Paid"
	elif flt(self.total_sanctioned_amount) > 0 and self.docstatus == 1 and self.approval_status == 'Approved':
		self.status = "Unpaid"
	elif self.docstatus == 1 and self.approval_status == 'Rejected':
		self.status = 'Rejected'