Question of the Day #6 [Talk::Overflow]

#webdev #programming #javascript #beginners

This post explains a quiz originally shared as a LinkedIn poll.

🔹 The Question

const scores = [8, 80, 9, 100, 15];
scores.sort();
console.log(scores);
console.log(scores[0] < scores[4]);

Hint: Consider how sort() compares values when no comparator function is provided.

🔹 Solution

Correct Answer: B) [100, 15, 8, 80, 9] and false

The output is:

[100, 15, 8, 80, 9]
false

🧠 How this works

This is one of JavaScript's most counterintuitive behaviors. When you call Array.prototype.sort() without a comparator function, all elements are converted to strings and sorted lexicographically (dictionary order), not numerically.

Lexicographic comparison works character by character from left to right:

'100' comes before '15' because '1' equals '1', but '0' < '5'
'8' comes before '80' and '9' because '8' < '9' in Unicode
'80' comes before '9' because '8' < '9'

The sort produces [100, 15, 8, 80, 9] — completely wrong for numeric ordering!

For the second output: scores[0] is 100 and scores[4] is 9. The comparison 100 < 9 is a numeric comparison (both values are numbers), which correctly evaluates to false.

The irony: The "sorted" array has its largest element first and a smaller element last, yet scores[0] < scores[4] returns false because numeric comparison works correctly — it's only the sort that's broken.

🔍 Line-by-line explanation

const scores = [8, 80, 9, 100, 15] — creates an array of numbers
scores.sort() — sorts in place using string comparison:
- Each number is converted to a string: ['8', '80', '9', '100', '15']
- Strings are compared character by character (Unicode code points)
- '1' (code 49) < '8' (code 56) < '9' (code 57)
- Result: ['100', '15', '8', '80', '9'] → converted back: [100, 15, 8, 80, 9]
console.log(scores) → [100, 15, 8, 80, 9]
console.log(scores[0] < scores[4]) → 100 < 9 → false

The misleading part: Developers expect sort() to "just work" on numbers like it does in most other languages. JavaScript's design choice to stringify first makes sense for mixed-type arrays but creates this gotcha for numeric arrays.

🔹 The Fix

Always provide a comparator for numeric sorting:

// Ascending order
scores.sort((a, b) => a - b);
// Result: [8, 9, 15, 80, 100]

// Descending order
scores.sort((a, b) => b - a);
// Result: [100, 80, 15, 9, 8]

🔹 Key Takeaways

Array.sort() without arguments converts elements to strings and sorts lexicographically
This affects all non-string types: numbers, dates, booleans, objects (which become '[object Object]')
Always provide a comparator function for numeric sorting: (a, b) => a - b
sort() mutates the original array—it doesn't return a new one
This is one of JavaScript's most common production bugs, especially when code works in testing with small sample data

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