Imperative-showTotalPrice.js

//imperative
//Returns error or price including tax 
const tax = (tax, price) => {
  if (!_.isNumber(price)) return new Error("Price must be numeric");

  return price + (tax * price);
};

//Returns error or price indluding discount
const discount = (dis, price) => {
  if (!_.isNumber(price)) return (new Error("Price must be numeric"));

  if (price < 10) return new Error("discount cant be applied for items priced below 10");

  return price - (price * dis);
};

const isError = (e) => e && e.name == 'Error';

const getItemPrice = (item) => item.price;

//shows total price after tax and discount. Need to handle multiple errors.
const showTotalPrice = (item, taxPerc, disount) => {
  let price = getItemPrice(item);
  let result = tax(taxPerc, price);
  if (isError(result)) {
    return console.log('Error: ' + result.message);
  }
  result = discount(discount, result);
  if (isError(result)) {
    return console.log('Error: ' + result.message);
  }
  //display result
  console.log('Total Price: ' + result);
}

let tShirt = { name: 't-shirt', price: 11 };
let pant = { name: 't-shirt', price: '10 dollars' };
let chips = { name: 't-shirt', price: 5 }; //less than 10 dollars error

showTotalPrice(tShirt) // Total Is: 9.075
showTotalPrice(pant)   // Error: Price must be numeric
showTotalPrice(chips)  //Error: discount cant be applied for items priced below 10

Note that you call showTotalPrice with a single parameter, where it expects 3 (item, taxPerc, disount)