How to Capitalize the First Letter of Each Word in an Array in JavaScript

To capitalize the first letter of each word in an array in JavaScript:

1. Iterate over the words array with .map().
2. For each word, return a new word, the uppercased form of the word’s first letter added to the rest of the word.

For example:

function capitalizeWords(arr) {
  return arr.map((word) => {
    const capitalizedFirst = word.charAt(0).toUpperCase();
    const rest = word.slice(1).toLowerCase();
    return capitalizedFirst + rest;
  });
}

const words = ['welcome', 'to', 'CODING', 'Beauty'];

// [ 'Welcome', 'To', 'Coding', 'Beauty' ]
console.log(capitalizeWords(words));

Our capitalizeWords() function takes an array of words and returns a new array with all the words capitalized, without mutating the original array.

Firstly, we call the map() method on the array, passing a callback function as an argument. This function will be called and return a result for each word in the array.

In the callback, we get the word’s first character with charAt(), convert it to uppercase with toUpperCase(), and concatenate it with the rest of the string.

We use the String slice() method to get the remaining part of the string. Passing 1 to slice() makes it return the portion of the string from the second character to the end.

Note: String (and array) indexing is zero-based JavaScript, so the first character in a string is at index 0, the second at 1, and the last at str.length-1

After capitalizing the word, we lowercase it with the String toLowerCase() method. You can remove this toLowerCase() call if it’s not necessary for the non-first letter of each word in the array to be capitalized.

Every Crazy Thing JavaScript Does

A captivating guide to the subtle caveats and lesser-known parts of JavaScript.