Computing the total

Sum each product's price with a loop to find the cart total.

The accumulator pattern

To sum the numbers in an array, you use the accumulator pattern:

Declare a total variable and set it to zero: let total = 0;
Inside the loop, add each value to total: total += price;
When the loop ends, total holds the sum of all values.

The += operator means "add the right value to the left": total += 5 is the same as total = total + 5.

Computing the cart total

To sum the prices of the products in the cart:

Initialize the accumulator with let total = 0;
Loop through each index in the cart with a for loop.
At each step, add the price with total += productPrices[cart[i]];

Here cart[i] is the product index at position i in the cart; productPrices[cart[i]] gives that product's price. We use two nested indexes.

Exercise Compute the cart total

Declare a let total = 0; variable. Then loop over the cart with a for loop and add each product's price to total (total += productPrices[cart[i]]). After the loop, print the total with console.log.

Show example solution

// Empty array for the cart
const cart = [];
// Product names and prices
const productNames = ["Pen", "Notebook", "Eraser"];
const productPrices = [15, 30, 10];
// Add products to the cart
cart.push(0);
cart.push(2);
// List the products in the cart
for (let i = 0; i < cart.length; i++) {
  console.log(productNames[cart[i]], productPrices[cart[i]]);
}
// Compute the total
let total = 0;
for (let i = 0; i < cart.length; i++) {
  total += productPrices[cart[i]];
}
console.log("Total:", total);

Test yourself

What should the initial value of an accumulator be?
- An empty array: []
- 1, because the first product's price is already counted
- The price of the first product in the cart
- 0, because summation starts from zero
Show answer

0, because summation starts from zero — Correct! Summation starts at zero and grows with each + step.

Update the total

let total = 0;
____
console.log("Total:", total);

Show answer

let total = 0;
total += productPrices[0];
console.log("Total:", total);

Match the accumulator pattern

let total = 0

Initial value of the accumulator
total += ...

Updates the total each step
for (let i = 0; ...)

Iterates over the array
console.log(total)

Prints the result

Next lesson: Project final - Shopping cart

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies