Course outline
Full-Stack course / JavaScript fundamentals

Swap the boxes

Lab

How to fetch and submit this exercise

Once: install the tool and connect your account.

curl -fsSL https://gonomicon.com/install.sh | sh
gonomicon login

Each exercise: download it, edit the file named in the instructions, then submit.

gonomicon fetch fs-week-2/01-01-swap-the-boxes
cd 01-01-swap-the-boxes
gonomicon submit

The runner depends on the exercise: JavaScript/TypeScript/React labs run with Vitest, Python labs with pytest, and config-file labs (Docker, CI, Terraform, Nginx) are checked by parsing your file. gonomicon test runs the visible checks on your computer first; submitting also runs the hidden checks on our server.

Swap the boxes

Goal: swap what two let variables hold, without typing their values again, and record whether the swap changed anything.

Worked example

The file starts with two boxes:

let first = 1;
let second = 2;

After your code runs, first holds 2, second holds 1, and a new const box called changed holds true, because the two originals were different.

Starting firstStarting secondfirst ends assecond ends aschanged
1221true
"a""a""a""a"false
5"5""5"5true

The last row is there on purpose: the number 5 and the text "5" are different shapes, so they count as different.

Rules

  • Keep the two lines at the top of the file as they are: let first = ...; and let second = ...;. The tests replace the values on those two lines and run your code with other values, so don't type the starting values anywhere else.
  • Write your code below those two lines.
  • Declare changed with const. Compare the two original values strictly.
  • Don't use var anywhere.
  • To look at your boxes while you work, add console.log(first, second, changed); at the bottom and run node swap_the_boxes.js.

What you'll practice

  • Making and changing let boxes, and making a const box
  • Strict equality between different shapes of value
  • Thinking about the order of your lines

Run it

gonomicon fetch fs-week-2/01-01-swap-the-boxes
cd 01-01-swap-the-boxes
gonomicon test
gonomicon submit

Hints

  1. A box holds one thing at a time. If you put the contents of second into first, what happens to what first was holding?
  2. You need a third box to park one value while you move the other. Work out changed before you start moving things, while both original values are still in their boxes.
  3. Start with const changed = first !== second;. Then park first in a new box, put second into first, and put the parked value into second.
PreviousNext lesson