convertHexadecimalToDecimal()

Step 1: Understanding the Concept

Before we begin coding, here's some essential background information. A hexadecimal number is a number system with base 16. It includes the digits 0-9 and the letters A-F where A is equivalent to decimal 10, B is 11, till F which is 15. We want to convert this into a decimal, a number system with base 10 (0-9).

Step 2: Initialize Variable

We'll start with creating a function convertHexadecimalToDecimal accepting a single parameter that represents the hexadecimal number.

function convertHexadecimalToDecimal(hex) {
    let decimal = 0;
}

Step 3: Process the hexadecimal string

Next, we will iterate over the hexadecimal string in reverse. The reasoning behind this is that the least significant digit (the rightmost one) has '2^0' weightage, the second least significant digit has '2^1', and so on until the most significant digit (the leftmost one).

function convertHexadecimalToDecimal(hex) {
    let decimal = 0;

    for(let i = hex.length - 1; i >= 0; i--) {
        // To be completed next...
    }
}

Step 4: Convert each digit to decimal and add to total

Up until now, we've just skimmed through the hex number in reverse. Now, at every step of the iteration, we will convert the ith digit to a decimal number and add it to our total (named 'decimal'). For digits that are alphabets, we will subtract 55 from their ASCII equivalent (as ASCII value of 'A' is 65 and 'A' represents 10 in hexadecimal, so 65-55 equals 10, and so on).

function convertHexadecimalToDecimal(hex) {
    let decimal = 0;

    for(let i = hex.length - 1; i >= 0; i--) {
        let digit = Number(hex.charAt(i));
        if(isNaN(digit)) {
            digit = hex.charCodeAt(i) - 55;
        }
        decimal += digit * Math.pow(16, hex.length - 1 - i);
    }

    return decimal;
}

That's it! We've completed our function.

Conclusion

So here we have our function to convert a hexadecimal number to a decimal one. Remember that the input for the function is a string representing a hexadecimal number, and the output is a number representing the corresponding decimal number. If the input string has a character that is not a valid hexadecimal character, our code will not handle it properly, so make sure you input valid hexadecimal numbers only! Our function uses the built-in JavaScript functions isNaN, charCodeAt and Math.pow to handle the necessary conversions and calculations.