Array .sort() / reverse()

// Sorts the array. The original array is modified.
array.sort();
array.sort(function(a, b) { return comparisonResult; });

// Reverses the array. The original array is modified.
array.reverse();

// Returns a new sorted array without modifying the original.
var newArray = array.toSorted(function(a, b) { return comparisonResult; });

// Returns a new reversed array without modifying the original.
var newArray = array.toReversed();

// Sorting strings
var fruits = ["Banana", "Apple", "Orange"];
fruits.sort();
console.log(fruits); // Outputs 'Apple,Banana,Orange' — sorted in Unicode order.

// Sorting numbers requires a comparison function.
var numbers = [10, 1, 21, 2];
numbers.sort(function(a, b) {
	return a - b; // Ascending order
});
console.log(numbers); // Outputs '1,2,10,21'.

// Sorting in descending order
numbers.sort(function(a, b) {
	return b - a;
});
console.log(numbers); // Outputs '21,10,2,1'.

// Reversing an array.
var letters = ["A", "B", "C", "D"];
letters.reverse();
console.log(letters); // Outputs 'D,C,B,A'.

// Using toSorted() to preserve the original array.
var original = [3, 1, 4, 1, 5];
var sorted = original.toSorted(function(a, b) {
	return a - b;
});
console.log(sorted); // Outputs '1,1,3,4,5'.
console.log(original); // Outputs '3,1,4,1,5' — the original array is unchanged.

When you call array.sort() without a comparison function, elements are converted to strings and sorted in Unicode order. For numeric arrays, this means [10, 1, 21, 2] would be sorted as [1, 10, 2, 21] — as strings rather than numbers. To sort numbers correctly, you need a comparison function such as function(a, b) { return a - b; }.

The comparison function takes two arguments. If the return value is negative, the first argument comes first; if positive, the second argument comes first; if zero, the order is unchanged. Returning a - b gives ascending order and b - a gives descending order — this pattern also works for sorting arrays of objects by a specific property.

array.sort() and array.reverse() are destructive methods that modify the original array directly. If you need to preserve the original, use toSorted() and toReversed() (added in ES2023), or copy the array with array.slice() before sorting.