JavaScript sort callback

The Sort

JavaScript Array.sort default algorithm:

• Firefox (SpiderMonkey engine): Merge Sort¹
• Chromium/Node (V8 engine): Tim Sort ²

The callback

Sort callback: comparefn(a, b)

The sort must be stable (that is, elements that compare equal must remain in their original order). If comparefn is not undefined, it should be a function that accepts two arguments x and y and returns a negative Number if x < y, a positive Number if x > y, or a zero otherwise.

• ECMAScript Language Specification³

So the comparefn expect you to return negative number, zero, or positive number. But you can return any other type without any error (runtime or default linter setting).

Firefox and Chromium/Node have a difference arguments order (reversed):

Left is firefox console, right is edge console.