Sorting an array

The sort method modifies an array in place (i.e. it does not create a new array) by arranging elements according to an ordering function.

An ordering function returns a number which indicates the relative ordering of two values.

const array = [8, 10, 5, 1, 7, 4, 3]
function ordering(a: number, b: number) {
    if (a > b) return 1
    if (a < b) return -1     
    return 0 // a == b
}
const sorted = array.sort(ordering)
console.log(sorted)
console.log(array)

Notice that array was modified by the sort operation as well. We can prevent this behavior by first copying to a new array, then sorting the resulting array.

const array = [4, 1, 3, 2]
const sorted = Array.from(array).sort((a, b) => (a - b))
console.log(array, sorted)

TypeScript also provides a Readonly type guard which can ensure that an array is not modified.

function sortNumbers(array: Readonly<Array<number>>) {
  return array.sort((a, b) => a - b)
}