Make a rule you can test

IDEA 1

Visit items in a list

An array is an ordered list. A rooms array might contain several room objects. for...of visits each object in order, giving the current object a temporary name such as room.

This loop is bounded by the array's length. Returning from inside it ends the function as soon as a suitable room is found. That implements ‘first suitable room,’ which is a specific selection rule rather than ‘best room.’

Scan without skipping

1. First. Maple has 10 seats; compare it with the request.
2. Next. Cedar has 20 seats; the same rule is applied again.
3. Stop. A return sends the first matching ID to the caller.

Three fictional rooms illustrate the order; only visited entries are inspected.

One name, successive objects

for (const room of input.rooms) {
  console.log(room.id);
}

Each iteration binds room to the next element. Logging an ID shows traversal, but choosing a room still needs a condition.

Think it through: If the first room passes and the function returns it, how many later rooms are visited?

IDEA 2

Compare values, including exact boundaries

A comparison returns true or false. seats >= people means capacity is at least the requested headcount. seats > people means strictly more seats, so it rejects an exact fit.

The && operator requires both conditions to pass. A room must be available and large enough. The case data uses explicit booleans for availability; do not infer availability from a friendly room name.

Two gates, one choice

1. Available?. A false value rejects the room regardless of size.
2. Enough seats?. Exactly 20 meets at least 20.
3. Both?. Only a room passing both conditions can be returned.

For 20 people, equal capacity satisfies the requirement.

Change one symbol, change the boundary

20 > 20  // false
20 >= 20 // true
19 >= 20 // false

Test below the boundary, exactly at it, and above it. The middle case catches an easy off-by-one-style requirement error.

Think it through: A free room seats 18 and the group has 18 people. Under an ‘at least’ rule?

IDEA 3

Handle an empty result

An empty array has no elements, so the loop body never runs. A nonempty array can also have no suitable room. Both situations need an honest no-match result.

We use null to mean ‘no room selected.’ Returning an invented ID would make the next part of the system act on a room it never found. Put return null after the loop so every candidate gets a chance first.

No match is a valid outcome

1. Inspect. A 12-seat room cannot fit 20 people.
2. Exhaust. The finite list ends without a passing entry.
3. Report. Return the agreed absence value.

A clear absence is more useful than an unsupported recommendation.

Placement changes behavior

for (const room of input.rooms) {
  if (room.available && room.seats >= input.people) return room.id;
}
return null;

null belongs after the loop. Putting it inside the loop after the first failed room would stop the search too soon.

Think it through: Why put return null after the loop?

Put it into practice

Return the first available room ID with enough seats, or null.

1. Read the people count and room order in each case.
2. Run the starter to observe its no-match baseline.
3. Replace the false condition with the availability and capacity rule.
4. Try an exact fit, then an empty room list.

Your next experiment: Make both rooms unavailable. Can you explain null without calling it an error?

Make the selection rule explicit, test equality, and give no match its own honest value.

Key terms

Array

An ordered list of values.

Condition

An expression whose true/false result controls which code runs.

null

An explicit absence value; here it means no room was selected.

Sources and scope

Original Stemtiq teaching, reviewed 2026-09-14. The named researchers and organizations do not endorse this course. Classroom cases are authored exercises, not published findings.