Converting to hex and summing the numeral part in JavaScript

We are required to write a JavaScript function that takes in a string, converts every character to its hex ASCII value, then sums only the numeric digits (0-9) from the hex representation, ignoring letters (a-f).

Problem

Given a string, we need to:

• Convert each character to its ASCII code
• Convert ASCII codes to hexadecimal
• Extract only numeric digits from the hex strings
• Sum all the numeric digits

Example

Let's see how this works with a complete example:

const str = "Hello, World!";
const toHexAndSum = (str = '') => {
    return str
        .split('')
        .map(c => c.charCodeAt())
        .map(n => n.toString(16))
        .join('')
        .split('')
        .filter(c => '0123456789'.includes(c))
        .map(d => parseInt(d))
        .reduce((a, b) => a + b, 0)
};
console.log(toHexAndSum(str));

91

Step-by-Step Breakdown

Let's trace through the process to understand how it works:

const str = "Hi!";
console.log("Original string:", str);

// Step 1: Split into characters
const chars = str.split('');
console.log("Characters:", chars);

// Step 2: Get ASCII codes
const asciiCodes = chars.map(c => c.charCodeAt());
console.log("ASCII codes:", asciiCodes);

// Step 3: Convert to hex
const hexValues = asciiCodes.map(n => n.toString(16));
console.log("Hex values:", hexValues);

// Step 4: Join and split to get individual hex digits
const hexString = hexValues.join('');
console.log("Joined hex:", hexString);

// Step 5: Filter only numeric digits
const numericDigits = hexString.split('').filter(c => '0123456789'.includes(c));
console.log("Numeric digits:", numericDigits);

// Step 6: Sum the digits
const sum = numericDigits.map(d => parseInt(d)).reduce((a, b) => a + b, 0);
console.log("Sum:", sum);

Original string: Hi!
Characters: [ 'H', 'i', '!' ]
ASCII codes: [ 72, 105, 33 ]
Hex values: [ '48', '69', '21' ]
Joined hex: 486921
Numeric digits: [ '4', '8', '6', '9', '2', '1' ]
Sum: 30

Alternative Implementation

Here's a more readable version with intermediate steps:

function toHexAndSumReadable(str) {
    let hexString = '';
    
    // Convert each character to hex
    for (let char of str) {
        const ascii = char.charCodeAt(0);
        const hex = ascii.toString(16);
        hexString += hex;
    }
    
    console.log(`Hex representation: ${hexString}`);
    
    // Sum only numeric digits
    let sum = 0;
    for (let char of hexString) {
        if (char >= '0' && char <= '9') {
            sum += parseInt(char);
        }
    }
    
    return sum;
}

console.log(toHexAndSumReadable("ABC"));

Hex representation: 414243
21

Key Points

• charCodeAt() returns the ASCII value of a character
• toString(16) converts decimal to hexadecimal
• Hex digits include 0-9 (numbers) and a-f (letters)
• We only sum the numeric portion (0-9), ignoring hex letters (a-f)

Conclusion

This function demonstrates string-to-hex conversion and selective digit summation. The key insight is filtering only numeric characters from the hex representation before performing the sum operation.