javascriptOtherMedium

Flattening stops after one level

Time: 0:00

BugFind the bug and fix the code

What it should do

flattenDeep(arr) removes all nesting, however deep. Example: flattenDeep([1, [2, [3, [4]]]]) → [1, 2, 3, 4].

What happens instead

flattenDeep([1, [2, [3, [4]]]]) returns [1, 2, [3, [4]]].

function flattenDeep(arr) {
    return arr.flat();
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the mutation and copying bugs pattern

Assignment does not copy, a shallow copy still shares its contents, and mutating methods return None.

Learn the mutation and copying bugs pattern Step through your own code

<iframe src="https://trybughunt.com/embed/71dfcd6c-94ee-4890-b3a1-5a56a682559e" title="Debugging challenge: Flattening stops after one level" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe> <p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/71dfcd6c-94ee-4890-b3a1-5a56a682559e">TryBugHunt</a></p>

javascriptOtherMedium

Flattening stops after one level

Time: 0:00

BugFind the bug and fix the code

What it should do

flattenDeep(arr) removes all nesting, however deep. Example: flattenDeep([1, [2, [3, [4]]]]) → [1, 2, 3, 4].

What happens instead

flattenDeep([1, [2, [3, [4]]]]) returns [1, 2, [3, [4]]].

function flattenDeep(arr) {
    return arr.flat();
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the mutation and copying bugs pattern

Assignment does not copy, a shallow copy still shares its contents, and mutating methods return None.

Learn the mutation and copying bugs pattern Step through your own code

Flattening stops after one level

What it should do

What happens instead

More mutation and copying bugs to practise

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Flattening stops after one level

What it should do

What happens instead

More mutation and copying bugs to practise

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