apply discount and exempt tax calculation for Canada

Question

The question was asked previously but there was not any proper answer. The problem is I am developing a POS application for a Canadian client. I am stuck in a tax calculation and could not be able to find a solution. So here is my scenario, I have 2 items lets say item 1 = $10 and item 2 = $2. The item 2 is tax exempted means the taxes (13%) will not be apply on item 2 but before applying tax. I need to apply discount for example of $5. So how to apply discount on my total bill and calculate the total tax.

I NEED A TAX AMOUNT AFTER DISCOUNT . THE TAX IS 13%.

Item 1 is $10 item 2 is $2 (Tax Exempt)

Subtotal is $12 Discount is $5 Tax will be ?

Answer 1

Here's one way to do it:

1. Sort the items by price, most expensive first.
2. Apply the discount to the items in the sorted list until no discount is left.
3. Sum the prices of that list to get the discounted subtotal.
4. Sum the prices of the taxable items in that list to get the taxable amount.
5. Apply the tax to the taxable amount, and add it to the subtotal to get the total.

const ITEMS = [
  { price: 2.00, taxExempt: true },
  { price: 10.00, taxExempt: false },
  { price: 8.25, taxExempt: false },
]
const DISCOUNT = 12
const TAX = 0.13

const applyDiscount = (items, discount) => {
  // 1️⃣ sort by price, most expensive to least
  items = items.slice().sort((a,b) => b.price - a.price)

  // 2️⃣
  return items.map(item => {
    let price = item.price
    const itemDiscount = Math.min(price, discount) 
    if (itemDiscount > 0) {
      price -= itemDiscount
      discount -= itemDiscount
    }
    return { ...item, price, origPrice: item.price, itemDiscount }
  })
}

const itemsWithDiscount = applyDiscount(ITEMS, DISCOUNT)
const sumPrices = arr => arr.map(x => x.price).reduce((p,c) => p + c, 0)
const subtotal = sumPrices(itemsWithDiscount) // 3️⃣
const taxableAmt = sumPrices(itemsWithDiscount.filter(x => !x.taxExempt)) // 4️⃣
const total = subtotal + (taxableAmt * TAX) // 5️⃣

console.log('items after discount', itemsWithDiscount)
console.log('subtotal: $' + subtotal.toFixed(2) + ' (taxable: $' + taxableAmt.toFixed(2) + ')')
console.log('tax: $' + (taxableAmt * TAX).toFixed(2) + ' (' + (TAX * 100) + '%)')
console.log('total: $' + total.toFixed(2))