Finding word starting with specific letter in JavaScript

Finding words that start with a specific letter is a common requirement in JavaScript applications. This guide shows different approaches to locate the first array element beginning with a specified character.

Problem Statement

We need to write a JavaScript function that takes an array of strings and a character, then returns the index of the first string starting with that character.

Using substring() Method

The substring() method extracts the first character for comparison:

const names = ['Naman', 'Kartik', 'Anmol', 'Rajat', 'Keshav', 'Harsh', 'Suresh', 'Rahul'];

const firstIndexOf = (arr = [], char = '') => {
    for(let i = 0; i < arr.length; i++){
        const el = arr[i];
        if(el.substring(0, 1) === char){
            return i;
        };
    };
    return -1;
};

console.log(firstIndexOf(names, 'K'));  // Found 'Kartik' at index 1
console.log(firstIndexOf(names, 'R'));  // Found 'Rajat' at index 3
console.log(firstIndexOf(names, 'J'));  // Not found, returns -1

1
3
-1

Using charAt() Method

The charAt() method provides a cleaner way to access the first character:

const findWordStartingWith = (arr, char) => {
    for(let i = 0; i < arr.length; i++){
        if(arr[i].charAt(0) === char){
            return i;
        }
    }
    return -1;
};

const fruits = ['apple', 'banana', 'cherry', 'orange', 'grape'];
console.log(findWordStartingWith(fruits, 'c'));  // Found 'cherry'
console.log(findWordStartingWith(fruits, 'o'));  // Found 'orange'
console.log(findWordStartingWith(fruits, 'z'));  // Not found

2
3
-1

Using findIndex() Method

For a more functional approach, use the built-in findIndex() method:

const animals = ['cat', 'dog', 'elephant', 'fox', 'giraffe'];

const findByFirstLetter = (arr, char) => {
    return arr.findIndex(word => word.charAt(0) === char);
};

console.log(findByFirstLetter(animals, 'd'));  // Found 'dog'
console.log(findByFirstLetter(animals, 'f'));  // Found 'fox'
console.log(findByFirstLetter(animals, 'z'));  // Not found

1
3
-1

Case-Insensitive Search

To handle both uppercase and lowercase letters, convert to lowercase before comparison:

const countries = ['India', 'japan', 'Canada', 'brazil'];

const findCaseInsensitive = (arr, char) => {
    return arr.findIndex(word => word.charAt(0).toLowerCase() === char.toLowerCase());
};

console.log(findCaseInsensitive(countries, 'j'));  // Found 'japan'
console.log(findCaseInsensitive(countries, 'B'));  // Found 'brazil'
console.log(findCaseInsensitive(countries, 'i'));  // Found 'India'

1
3
0

Comparison

Conclusion

Use charAt(0) for the best performance and readability when finding words starting with specific letters. The findIndex() method offers a more functional approach for modern JavaScript applications.