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reverse() in JS – How to Reverse a JavaScript Array

Whenever you use reverse() on an array, the method does the following:

  1. It reverses the array so that its first item becomes the last and its last element becomes the first.
  2. It returns a reference to the reversed-original array.
note
  • reverse() is a destructive method that alters the original array.
  • reverse() is sometimes written as Array.prototype.reverse() because it is a method of the Array object's prototype property.

Syntax of the reverse() Method​

reverse() accepts no argument. Here is the syntax:

arrayObject.reverse();

Examples​

Below are examples of the reverse() method.

How to reverse an array of three items​

// Define an array:
const numbersArray = [1, 2, 3];

// Reverse the numbersArray:
const reversedArray = numbersArray.reverse();

// Log the reversedArray to the console:
console.log(reversedArray);

// The invocation above will return: [3, 2, 1]

Try it on StackBlitz

The snippet above used reverse() to reorder numbersArray's elements so that its first item (1) becomes the last and its last element (3) becomes the first.

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How to reverse an array of five items​

// Define an array:
const colorsArray = ["Blue", "Green", "Indigo", "Lime", "Orange"];

// Reverse the colorsArray:
const reversedArray = colorsArray.reverse();

// Log the reversedArray to the console:
console.log(reversedArray);

// The invocation above will return: ["Orange", "Lime", "Indigo", "Green", "Blue"]

Try it on StackBlitz

The snippet above used reverse() to reverse colorsArray's layout.

Important Stuff to Know about the reverse() Method​

Here are two essential facts to remember when using the reverse() method.

1. reverse() does shallow copy​

reverse() returns a shallow copy of the original array. In other words, reverse() creates a reference between the returned array and its original.

Therefore, changes to the returned array will also reflect in the original.

Here's an example:

const numbersArray = [1, 2, 3];
const reversedArray = numbersArray.reverse();

console.log(numbersArray); // [3, 2, 1]
console.log(reversedArray); // [3, 2, 1]

// Add 2500 to the end of the reversedArray:
reversedArray.push(2500);

console.log(reversedArray); // [3, 2, 1, 2500]
console.log(numbersArray); // [3, 2, 1, 2500]

Try it on StackBlitz

You can see that mutating the reversedArray also changed the original array because reverse() returned a shallow copy of numbersArray.

note

You can use the spread syntax to make reverse() do a deep copy of the original array. But beware of how spread works on objects containing non-primitives.

2. reverse() reverses empty slots​

reverse() treats empty array slots like other filled indices.

Here's an example:

const numbersArray = [1, 2, , 3];
const reversedArray = numbersArray.reverse();

console.log(reversedArray); // [3, empty, 2, 1]

Try it on StackBlitz

You can see that reverse() reversed the empty slot's position like other filled indices.

Overview​

reverse() reverses an array so that its first item becomes the last and its last element becomes the first.

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