javascriptScope errorMedium

Object freeze is shallow and allows nested settings mutation

Time: 0:00

BugFind the bug and fix the code

What it should do

protect_nested_config(config, newPort) prevents mutating nested configuration properties on config. Example: protect_nested_config({ database: { port: 5432 } }, 9999) → 5432.

What happens instead

Calling protect_nested_config mutates config.database.port in place because Object.freeze is shallow.

function protect_nested_config(config, newPort) {
  const frozen = Object.freeze(config);
  frozen.database.port = newPort;
  return frozen.database.port;
}

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

⏱️0:00

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Hint 3

Unlocks after Hint 2

This bug belongs to the scope and closure bugs pattern

Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.

Learn the scope and closure bugs pattern Step through your own code

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javascriptScope errorMedium

Object freeze is shallow and allows nested settings mutation

Time: 0:00

BugFind the bug and fix the code

What it should do

protect_nested_config(config, newPort) prevents mutating nested configuration properties on config. Example: protect_nested_config({ database: { port: 5432 } }, 9999) → 5432.

What happens instead

Calling protect_nested_config mutates config.database.port in place because Object.freeze is shallow.

function protect_nested_config(config, newPort) {
  const frozen = Object.freeze(config);
  frozen.database.port = newPort;
  return frozen.database.port;
}

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 scope and closure bugs pattern

Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.

Learn the scope and closure bugs pattern Step through your own code

Object freeze is shallow and allows nested settings mutation

What it should do

What happens instead

More scope and closure bugs to practise

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Object freeze is shallow and allows nested settings mutation

What it should do

What happens instead

More scope and closure bugs to practise

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