Replace a letter with its alphabet position JavaScript

We are required to write a function that takes in a string, trims it off any whitespaces, converts it to lowercase and returns an array of numbers describing corresponding characters positions in the english alphabets, any whitespace or special character within the string should be ignored.

Problem Example

Input ? 'Hello world!'
Output ? [8, 5, 12, 12, 15, 23, 15, 18, 12, 4]

How It Works

The algorithm processes each character by:

• Converting to lowercase to handle both cases uniformly
• Getting ASCII code using charCodeAt()
• Checking if it's a letter (ASCII 97-122 for a-z)
• Converting ASCII to alphabet position by subtracting 96

Implementation

const str = 'Hello world!';

const mapString = (str) => {
    const mappedArray = [];
    str
    .trim()
    .toLowerCase()
    .split("")
    .forEach(char => {
        const ascii = char.charCodeAt();
        if(ascii >= 97 && ascii <= 122){
            mappedArray.push(ascii - 96);
        };
    });
    return mappedArray;
};

console.log(mapString(str));

[
  8, 5, 12, 12, 15,
  23, 15, 18, 12, 4
]

Alternative Approach Using Regular Expressions

const mapStringRegex = (str) => {
    return str
        .toLowerCase()
        .replace(/[^a-z]/g, '')  // Remove non-letters
        .split('')
        .map(char => char.charCodeAt(0) - 96);
};

console.log(mapStringRegex('Hello world!'));
console.log(mapStringRegex('Programming123'));

[ 8, 5, 12, 12, 15, 23, 15, 18, 12, 4 ]
[ 16, 18, 15, 7, 18, 1, 13, 13, 9, 14, 7 ]

Method Comparison

Key Points

• ASCII values: 'a' = 97, 'z' = 122
• Alphabet position = ASCII code - 96
• Non-alphabetic characters are filtered out
• Case-insensitive processing via toLowerCase()

Conclusion

Both approaches effectively convert letters to their alphabet positions while filtering non-alphabetic characters. The forEach method offers explicit control, while the regex approach provides cleaner, more functional code.