JavaScript Program to Test if Kth Character is Digit in String

In this article, we are Given a String, we will check if the K^th index element is a digit or not. If it is a digit then we will print true else we will print false.

Examples:

Input : test_str = ‘geeks9geeks’, K = 5 
Output : True 
Explanation : 5th idx element is 9, a digit, hence True.
Input : test_str = ‘geeks9geeks’, K = 4 
Output : False 
Explanation : 4th idx element is s, not a digit, hence False. 

These are the following approaches by using these we can check whether the digit is present at the K^th index or not:

Using charAt():

In this approach, we check if the character at the Kth index in a string is a digit. It uses the ‘charAt’ method to retrieve the character at the specified index and the ‘includes’ method to check if the character exists in the numeric string “0123456789”. The result is a boolean indicating whether the Kth element is a digit in the string.

Example: This example shows the use of the above-explained approach.

Javascript

// Initializing string
let test_str = 'geeksgeeks';

// Printing original string
console.log("The original string is : " + test_str);

// initializing K
let K = 5;

// Checking if Kth character is a
// digit in the string

// Getting numeric string
let num_str = "0123456789";
let res = num_str.includes(test_str.charAt(K));

// Printing result
console.log("Is Kth element String : " + res);

Output

The original string is : geeksgeeks
Is Kth element String : false

Using regular expression:

In this approach, we are using the ‘match’ method to check if the character at the K^thj index in a string matches the regular expression pattern for a single digit `\d`. It stores the result in a boolean variable ‘res’ using the double negation ‘!!’ to convert the match result to a boolean value. Finally, it prints whether the K^th element is a digit in the string.

Example: This example shows the use of the above-explained approach.

Javascript

// Initialize string
let test_str = 'geeks4geeks';

// Print original string
console.log("The original string is : " + test_str);

// Initialize K
let K = 5;

// Regular expression pattern for a single digit
let pattern = /\d/;

// Check if the Kth character
// matches the pattern
let match = test_str.charAt(K).match(pattern);

// Set the value of res based on the match result
let res = !!match;

// Print result
console.log("Is Kth element String : " + res);

Output

The original string is : geeks4geeks
Is Kth element String : true

Using loop

This approach iterates over each character in the string and checks if the current index matches the kth position. If it does, it checks if the character is a digit. If the character is a digit it returns true otherwise, it returns false.

Example: This example shows the use of the above-explained approach.

JavaScript

function isKthCharacterDigit(str, k) {
    for (let i = 0; i < str.length; i++) {
        if (i === k - 1) {
            return /\d/.test(str[i]);
        }
    }
    // Return false if k is out of bounds
    
    return false; 
}

let string = "geeks57f2orgeeks";
let k = 5;
console.log(`Is the ${k}th character a digit: ${isKthCharacterDigit(string, k)}`);

Output

Is the 5th character a digit: false