Decimal numbers are a base 10 number system which uses 10 digits from 0 to 9 and hexadecimal numbers are a base 16 number system which uses 16 digits, numbers from 0 to 9, and letters from A to F. We are given a hexadecimal number as input we have to convert it into decimal in JavaScript and print the result.

Example:

Input: 1A
Output: 26

Below are the methods to convert Hexadecimal to Decimal:

Using parseInt() Function

In this approach, there is an inbuilt function parseInt which will convert the hexadecimal number into its decimal equivalent. Use the ‘parseInt’ function with base 16 to convert hexadecimal to decimal to convert the hexadecimal string to its decimal equivalent.

Example: Demonstration of converting of hexadecimal to decimal using the inbuilt parseInt().

function hexadeciToDeci(hex) {
    return parseInt(hex, 16);
}

//  Hexadecimal Number
const hexadecimalNumber = "2A";
const decimal = hexadeciToDeci(hexadecimalNumber);
console.log("Decimal equivalent of", 
             hexadecimalNumber, "is  ", decimal);

Decimal equivalent of 2A is   42

Time Complexity: O(n).

Space Complexity: O(1).

Using Number() Function

In this approach, we will use the built-in JavaScript function Number() to convert the concatenated string to a decimal number. JavaScript recognizes the hexadecimal format when the “0x” prefix is present inside the Number() function. We will return the decimal equivalent of the hexadecimal input.

Example: Demonstration of converting hexadecimal to decimal using the Number() function.

function hexaToDeci(hex) {

    // Using Number() function with base 16 
    return Number(`0x${hex}`);
}

// hexadecimal string
const hexadecimalNumber = "1A";
const decimal = hexaToDeci(hexadecimalNumber);
console.log("Decimal equivalent of  ",
    hexadecimalNumber, "is  ", decimal);

Decimal equivalent of   1A is   26

Time Complexity: O(n).

Space Complexity: O(1).

Using Iterative Method

In this approach, we will convert the hexadecimal to its decimal equivalent by first converting the current (each) hexadecimal digit to its decimal equivalent using the ‘parseInt’ inbuilt function and then update the decimal value by multiplying by 16 and adding the decimal value of the current digit.

Example: Below is the conversion of hexadecimal to decimal by iterating through each character of a hexadecimal string.

// Define the function 
function hexadeciToDeci(hex) {
    
    // Initialize Variable
    let decimal = 0;

    for (let i = 0; i < hex.length; i++) {

        // Convert the current hexadecimal digit
        let digit = parseInt(hex[i], 16);

        // Update the decimal value by multiplying by 16
        // Add the decimal value of the current digit
        decimal = decimal * 16 + digit;
    }

    return decimal;
}

//  hexadecimal number
const hexadecimalNumber = "1A";
const decimalEqui = hexadeciToDeci(hexadecimalNumber);
console.log(" The Decimal equivalent of", 
              hexadecimalNumber, "is : ", decimalEqui);

 The Decimal equivalent of 1A is :  26

Time Complexity: O(n)

Space Complexity: O(1)