Native `.sort()` Method

What is it

The native sort() method sorts the elements of an array "in place" and returns the sorted array

in-place means no copy is made

// string sort
const months = ['March', 'Jan', 'Feb', 'Dec'];
months.sort();

console.log(months);
// ["Dec", "Feb", "Jan", "March"];

// number sort
const array1 = [1, 30, 4, 21, 100000];
array1.sort();

console.log(array1);
// [1, 100000, 21, 30, 4];

Space/Time Complexity

The time and space complexity of the sort cannot be guaranteed as it depends on the implementation.

Default Behaviors

The default sort order is ascending

built upon converting the elements into strings
then comparing their sequences of UTF-16 code units values

Sorting Numbers

To compare numbers instead of strings, the compare function can subtract b from a. The following function will sort the array in ascending order (if it doesn't contain Infinity and/or NaN)

CompareFunction for numbers in ascending order

function compareNumbers(a, b) {
  return a - b;
}

const numbers = [4, 2, 5, 1, 3];

// function expressions
numbers.sort(function(a, b) {
  return a - b;
});
console.log(numbers); // [1, 2, 3, 4, 5];

// arrow function
numbers.sort((a, b) => a - b);
console.log(numbers); // [1, 2, 3, 4, 5];

How `Array.sort((a,b) ⇒ (a-b))` sorts numbers

The function that you pass tells how to sort the elements

It takes two parameters (a, b) that represent any two elements from the array

How the elements will be sorted depends on the function’s return value

If it returns a negative value, the value in a will be ordered before b
if it returns 0, the ordering of a and b won’t change
if it returns a positive value, the value in b will be ordered before a

Compare function deep dive

function compare(a, b) {
  if (a is less than b by some ordering criterion) {
    return -1;
  }
  if (a is greater than b by the ordering criterion) {
    return 1;
  }
  // a must be equal to b
  return 0;
}

Sorting non-ASCII Characters

For sorting strings with non-ASCII characters, i.e. strings with accented characters (e, é, è, a, ä, etc.), strings from languages other than English, use String.localeCompare

This function can compare those characters so they appear in the right order.

const items = ['réservé', 'premier', 'communiqué', 'café', 'adieu', 'éclair'];

items.sort(function (a, b) {
  return a.localeCompare(b);
});

console.log(items); // ['adieu', 'café', 'communiqué', 'éclair', 'premier', 'réservé'];

Sorting Array of Objects

Arrays of objects can be sorted by comparing the value of one of their properties

var items = [
  { name: 'Edward', value: 21 },
  { name: 'Sharpe', value: 37 },
  { name: 'And', value: 45 },
  { name: 'The', value: -12 },
  { name: 'Magnetic', value: 13 },
  { name: 'Zeros', value: 37 }
];

// sort by value
items.sort(function (a, b) {
  return a.value - b.value;
});

// sort by name
items.sort(function(a, b) {
  var nameA = a.name.toUpperCase(); // ignore upper and lowercase
  var nameB = b.name.toUpperCase(); // ignore upper and lowercase
  if (nameA < nameB) {
    return -1;
  }
  if (nameA > nameB) {
    return 1;
  }

  // names must be equal
  return 0;
});

Array Sort

Native .sort() Method