Why Math.max() Is Smaller Than Math.min()

The curse

console.log(Math.max()); // prints: -Infinity
console.log(Math.min()); // prints: Infinity
console.log(Math.max() < Math.min()); // prints: true

Call them with nothing inside, and max is smaller than min.

Why it happens

Math.max looks at its arguments one by one and keeps the biggest so far. Before it has seen anything, it needs a starting value that any number will beat. The only value that works for every possible number is -Infinity. When you pass nothing, nothing ever replaces that starting value, so it is what you get back.

Math.min is the mirror image. It starts at Infinity, since every number is smaller than that.

This choice keeps the math consistent. The biggest number in a group should not change when you add an empty group to it, and -Infinity is the only starting value that never wins against a real number.

console.log(Math.max(3, 7, 2)); // prints: 7
console.log(Math.max(-500)); // prints: -500

With an array

Math.max wants separate numbers, not a list. Don't forget the three dots.

const heights = [3, 7, 2];
console.log(Math.max(heights)); // prints: NaN
console.log(Math.max(...heights)); // prints: 7

When you pass the array itself, Math.max gets one argument and tries to turn it into a number. An array becomes text first, "3,7,2", and that text is not a number, so the result is NaN. The three dots of the spread operator unpack the array into separate arguments, so the call becomes Math.max(3, 7, 2).

There is a sneaky detail here. An array with one item, like [5], becomes the text "5" and then the number 5, so Math.max([5]) happens to work. Code like that can pass a quick test with one item and break as soon as there are two.

Bonus twist: empty arrays

Spreading an empty array is the same as passing nothing, so you are back to minus infinity.

const noKids = [];
console.log(Math.max(...noKids)); // prints: -Infinity

If your list can be empty, check before you trust the answer, and decide what "no answer" should look like in your program.

const scores = [];
const best = scores.length > 0 ? Math.max(...scores) : null;
console.log(best); // prints: null

One more practical tip. For very long arrays, hundreds of thousands of items, spreading can hit the engine's limit on how many arguments a function can take. For data that big, a plain loop or reduce is the safer choice.

Rule of thumb