Debug a JavaScript function together

A teammate has a shopping-cart total that joins strings instead of adding prices. Use one file for the function and another for examples, then work through the fix together.

Create a pad. Choose a display name if prompted. Set the language to JavaScript and rename the first tab to cart.js.
Invite your teammate. Open share, copy the edit link, and send it. They can open it in another browser without an account.
Add a second file. Use the new-file button to create examples.js. Write the inputs and expected results there.
Review the change. Start with string prices, discuss why JavaScript joins them, and convert each price to a number. Use the labeled cursors to follow each other.

// cart.js
export function subtotal(prices) {
  return prices.reduce((sum, price) => sum + Number(price), 0);
}

// examples.js
subtotal(['12.50', '7.50']); // Expected: 20
subtotal([]);               // Expected: 0

The comments show expected results. Codepad does not execute the function. Run it in your local JavaScript environment when you want to verify the output.

A staged Codepad session with cart.js and examples.js tabs, two collaborators, and the author’s private debugging notes. — An example session in Codepad. The code is shared; the notes on the right belong only to the person viewing this screen.

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