Use forEach() on an Array in Reverse Order in JavaScript

Use forEach() on an Array in Reverse Order #

To use the forEach() method on an array in reverse order:

1. Use the slice() method to get a copy of the array.
2. Use the reverse() method to reverse the copied array.
3. Call the forEach() method on the reversed array.

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const arr = ['a', 'b', 'c'];

arr
  .slice()
  .reverse()
  .forEach(element => {
    console.log(element); // 👉️ c, b, a
  });

The first step is to use the Array.slice method to create a shallow copy of the array.

We do this because the Array.reverse method changes the contents of the original array in place.

Calling the slice() method with no parameters returns a shallow copy of original array, which we can reverse.

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const arr = ['a', 'b', 'c'];

const copy = arr.slice();
console.log(copy); // 👉️ ['a', 'b', 'c']

The reverse() method reverses an array in place and returns the result.

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const arr = ['a', 'b', 'c'];

const reversed = arr.reverse();
console.log(reversed); // 👉️ ['c', 'b', 'a']

console.log(arr); // 👉️ ['c', 'b', 'a']

This is the reason we created a shallow copy in advance - to avoid changing the original array.

The last step is to use the Array.forEach method on the reversed array.

An alternative approach is to use the spread syntax (...) to create a shallow copy of the array.

To use the forEach() method on an array in reverse order:

1. Use the spread syntax (...) to get a copy of the array.
2. Use the reverse() method to reverse the copied array.
3. Call the forEach() method on the reversed array.

Copied!
const arr = ['a', 'b', 'c'];

[...arr].reverse().forEach(element => {
  console.log(element); // 👉️ c, b, a
});

The spread syntax (...) unpacks the values from the original array into a new array, creating a shallow copy.

We then reverse the copy to avoid mutating the original array and call the forEach() method on the reversed array.

Further Reading #

• Loop through Object in Reverse Order using JavaScript
• Swap the Keys and Values in an Object using JavaScript