Checkpoint: Recommendations

Your 15-minute checkpoint

Close the earlier examples. Spend two minutes writing the inputs, expected outputs, and steps in plain language. Use about eight minutes to build and test, then five to explain your choices and try the variation. Taking longer is normal: these are study budgets, not speed tests.

Compose filtering, ordering, and formatting. This problem deliberately changes the setting so you practise choosing the tools yourself.

A small warm-up

Before the main task, predict this familiar idea from today’s work. If it is unclear, revisit the relevant teaching lesson first.

Check the foundation

Say why each line appears, not just what it prints.

Check the foundation JavaScript

const double = value => value * 2;

console.log([2, 3].map(double).join(", "));

Check your prediction

4, 6

Use this only as a warm-up. The main task needs you to combine several decisions.

Acceptance cases before you code

Write a small test plan before implementing recommendation order and ownership. These cases extend the brief; they are not a second worked solution. Predict the expected behavior independently, then test through the public function. A good ordinary example and a good boundary example should catch different possible mistakes.

Case to try	What your result should demonstrate
No eligible session	Return empty text rather than reading an absent first item
Session exactly at the limit	Include it
Unsorted input with distinct durations	Return shortest-first names and preserve source order

After the core task passes, deliberately break one rule and identify the case that notices it. Restore the implementation and explain the failure in terms of the contract, not the number of assertions. If a case requires a concept you have not recalled, revisit the relevant lesson before opening the solution.

Exercise

A recommendation function

Write recommend(sessions, maxMinutes). Select sessions no longer than the limit, order them shortest first, and return topic names joined by a comma. Preserve the original order.

Your working space JavaScript

const sessions = [
  { topic: "Objects", minutes: 30 },
  { topic: "Loops", minutes: 10 },
  { topic: "Arrays", minutes: 20 }
];

Hint 1: the idea

Select records first, order the selected array, then transform records into names.

Hint 2: a first step

filter returns a new array; sort that result with a minutes comparator.

Show one solution

function recommend(sessions, maxMinutes) {
  const eligible = sessions.filter(item => item.minutes <= maxMinutes);
  const ordered = eligible.sort((a, b) => a.minutes - b.minutes);
  const topics = ordered.map(item => item.topic);

  return topics.join(", ");
}

const sessions = [
  { topic: "Objects", minutes: 30 },
  { topic: "Loops", minutes: 10 },
  { topic: "Arrays", minutes: 20 }
];

console.log(recommend(sessions, 20));
console.log(sessions[0].topic);

Loops, Arrays
Objects

Try limits of 9, 10, and 30. The first returns an empty string by this contract. Add a display fallback at the call site if needed.

Change the requirements