JavaScript - Index of a Character in String

The indexOf() method can be used to find the first index of specific character in a string. This function returns the index of the given character in a given string.

Using indexOf() - Most Used

The indexOf() method is a method to find the index of the first occurrence of a specific string within a string.

let s = "abcd";
let c = "c";
let index = s.indexOf(c);
console.log(index);

2

Using String lastIndexOf() Method

The lastIndexOf() method finds the index of the last occurrence of a specific character in a string. It works similarly to indexOf() but searches from the end of the string.

let s = "Welcome to GeeksforGeeks";
let c = "G";
let index = s.lastIndexOf(c);
console.log(index);

19

Using search() - Used for Regular Expressions

The search() method is a powerful tool used to search for a specific substring within a string. It returns the index of the first occurrence of the specified substring.

let s = "abcd";
let c = "c";
let index = s.search(c);
console.log(index);

2

Using match() - Used for Regular Expressions and More options

The match() method is used to search a string based on a specified pattern. It allows you to perform powerful string matching having options like global search, case insensitive search and provide detailed information.

let s = "abcd";
let c = "c";
let index = s.match(c);
console.log(index.index);

2

Writing your Own Method

In this approach, we can iterate over each character in the string using a for loop and check if it matches the specific character we are looking for. If a match is found, we return the index of that character. If no match is found, we return -1 to indicate that the character is not present in the string.

function findIndex(str, char) {
    for (let i = 0; i < str.length; i++) {
        if (str[i] === char) {
            return i;
        }
    }
    return -1; // Character not found
}

let str = "Welcome to GeeksforGeeks";
let char = "G";
let index = findIndex(str, char);
console.log(index);

11

Using ES6 findIndex() with Array.from() Method

In this approach, we can utilize ES6 features like Array.from() along with the findIndex() method to find the index of a specific character in a string. This method converts the string into an array of characters, then applies the findIndex() method to search for the desired character.

function findIndex(s, c) {

    // Convert string to array of characters
    let a = Array.from(s);
    
    // Find index of the character using findIndex method
    let index = a.findIndex((x) => x === c);
    
    return index;
}

let s = "abcd";
let c = "c";
let index = findIndex(s, c);
console.log(index); 

2