Simple JS program for buying a phone, Apply tax, format and add to cart.

purchase-phone.js

const TAX_RATE = 0.10;   // 10%
const PHONE_PRICE = 500; // $500
const ACCESSORY_PRICE = 12;  //$12
const SPENDING_THRESHOLD = 900;  // This should be 60% of the total bank balance.

var bank_account_balance = 0;
var quantity = 0;
var total = 0;

bank_account_balance = prompt("What is your Bank Account Balance");
quantity = prompt("One phone costs " + PHONE_PRICE + " How many you want to buy");

console.log(buy(PHONE_PRICE, quantity));

function buy( product, qty ){
	total = product * qty;
	total += tax_calculation(total)
	
	if( total > SPENDING_THRESHOLD){
		return "Warning! This is a threshold alert";
    }else if( total > bank_account_balance){
		return "Warning! You can't buy this phone. Please check your bank";
	}else{
		return "Your Purchase: " + format_price(total);
	}

	
}

function tax_calculation( amount ) {
	return amount * TAX_RATE;
}

function format_price( amount ){
	return '$' + amount.toFixed(2);
}