In JavaScript, does sort with (a,b) ⇒ b - a produce ascending or descending order? Why?

Answer

(a, b) => b - a sorts the array in descending order (largest to smallest).

How Sort Works

Array.prototype.sort() accepts a comparator compareFn(a, b) that controls ordering:

Return value	Behavior
Negative	a comes before b
0	Order unchanged
Positive	b comes before a

Analyzing b - a

• If b > a → returns positive → b comes first → larger value first → descending
• If b < a → returns negative → a comes first → larger value first → descending
• If b === a → returns 0 → order unchanged

Example

const arr = [3, 1, 4, 1, 5, 9, 2, 6];

// Ascending (a - b)
arr.sort((a, b) => a - b); // [1, 1, 2, 3, 4, 5, 6, 9]

// Descending (b - a)
arr.sort((a, b) => b - a); // [9, 6, 5, 4, 3, 2, 1, 1]

Memory Trick

• a - b → ascending (a goes first)
• b - a → descending (b goes first)