Convert all Array Elements to Lowercase in JavaScript

Convert all Array Elements to Lowercase #

To convert all array elements to lowercase:

1. Use the map() method to iterate over the array.
2. On each iteration, call the toLowerCase() method to convert the string to lowercase and return the result.
3. The map method will return a new array containing only lowercase strings.

Copied!
const arr = ['ONE', 'TWO', 'THREE'];

const lower = arr.map(element => {
  return element.toLowerCase();
});

console.log(lower); // 👉️ ['one', 'two', 'three']

The function we passed to the Array.map method gets called with each element (string) in the array.

The map method returns a new array containing all the values the callback function returned.

We used the String.toLowerCase method to convert each string in the array to lowercase.

An alternative, but also very commonly approach is to do this using the Array.forEach method.

To convert all array elements to lowercase:

1. Declare a new variable and set it to an empty array.
2. Use the forEach() method to iterate over the original array.
3. Convert each string to lowercase and push the strings into the new array.

Copied!
const arr = ['ONE', 'TWO', 'THREE'];

const lower = [];

arr.forEach(element => {
  lower.push(element.toLowerCase());
});

console.log(lower); // 👉️ ['one', 'two', 'three']

We used the Array.forEach method to convert all array elements to lowercase.

The function we passed to the forEach() method gets called with each element in the array.

Each element gets converted to lowercase and gets pushed into the new array.

This approach is a bit more manual and verbose. It's very similar to using a for loop.

The forEach method returns undefined, so we have to perform some kind of mutation to persist the state.

Further Reading #

• How to Modify all Array Elements in JavaScript
• Convert all Array Elements to Uppercase in JavaScript
• Trim all Strings in an Array using JavaScript
• Set all Array Elements to a Specific Value in JavaScript
• Convert a String to Array of Numbers in JavaScript
• Convert all Array Elements to Lowercase in JavaScript
• Convert all Array Elements to Uppercase in JavaScript
• Check if Multiple Values exist in Array in JavaScript
• Capitalize the First Letter of Each Word in Array in JS