javascriptNull / UndefinedMedium

Score total turns into NaN

Time: 0:00

BugFind the bug and fix the code

What it should do

sumScores(players) adds up every player's score. A player with no score counts as 0. Example: [{ score: 10 }, {}, { score: 5 }] → 15.

What happens instead

sumScores([{ score: 10 }, {}, { score: 5 }]) returns NaN.

function sumScores(players) {
    let total = 0;
    for (const player of players) {
        total += player.score;
    }
    return total;
}

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 null and undefined errors pattern

Cannot read properties of undefined, NoneType has no attribute, NaN appearing from nowhere.

Learn the null and undefined errors pattern Step through your own code

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javascriptNull / UndefinedMedium

Score total turns into NaN

Time: 0:00

BugFind the bug and fix the code

What it should do

sumScores(players) adds up every player's score. A player with no score counts as 0. Example: [{ score: 10 }, {}, { score: 5 }] → 15.

What happens instead

sumScores([{ score: 10 }, {}, { score: 5 }]) returns NaN.

function sumScores(players) {
    let total = 0;
    for (const player of players) {
        total += player.score;
    }
    return total;
}

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 null and undefined errors pattern

Cannot read properties of undefined, NoneType has no attribute, NaN appearing from nowhere.

Learn the null and undefined errors pattern Step through your own code

Score total turns into NaN

What it should do

What happens instead

More null and undefined errors to practise

Seen this error in your own code?

Score total turns into NaN

What it should do

What happens instead

More null and undefined errors to practise

Seen this error in your own code?