Basket summary

Goal: price a shopping basket with three functions: one with a default parameter and two that accept any number of prices through a rest parameter.

Worked example

The three functions

• withTax(price, percent) gives back the price plus percent percent of the price. If nobody says what the percent is, use 20.
• sumAll(...amounts) gives back the total of every number it was given, or 0 when it was given none.
• basketLine(label, ...prices) gives back a line of text: the label, an x, how many prices there were, an equals sign and the total of the prices. If nobody gives a label, use "Basket". Passing undefined as the label means "I'm not giving one".

Rules

• Write all three as function declarations, with exactly these names.
• withTax must use a default parameter. sumAll and basketLine must use a rest parameter, and must not use the old arguments object.
• Each function must return its answer rather than print it.
• Walk the list of prices with a loop.
• You can try things out with a line like console.log(basketLine("Gifts", 10, 20, 30)); at the bottom while you work, then remove it, and run node basket_summary.js.

What you'll practice

• A default parameter, and what it takes to trigger one
• A rest parameter collecting leftover arguments into a list
• Walking that list with for...of while keeping a running total
• Building one line of text with a template literal

Run it

gonomicon fetch fs-week-2/02-03-basket-summary
cd 02-03-basket-summary
gonomicon test
gonomicon submit

Hints

1. For withTax, put the default right in the parameter list: percent = 20. For the other two, a rest parameter (...amounts, ...prices) hands you every extra argument as a list you can walk with for...of.
2. Inside sumAll, make a let box that starts at 0 and add each amount to it in a for...of loop. basketLine needs the same total plus a count of how many prices came in, so keep two boxes going in one loop. The label slot comes first, so give it a default and put the rest parameter after it.
3. function withTax(price, percent = 20) { return price + price * percent / 100; }. For the other two: function sumAll(...amounts) { let total = 0; for (const amount of amounts) { total += amount; } return total; }, and basketLine works the same way with a counter, ending in return ${label} x${count} = ${total};.