Replacing upperCase and LowerCase in a string - JavaScript

We are required to write a JavaScript function that takes in a string and constructs a new string with all the uppercase characters converted to lowercase and all the lowercase characters converted to uppercase.

Let's write the code for this function ?

Example

Following is the code ?

const str = 'The Case OF tHis StrinG Will Be FLiPped';
const isUpperCase = char => char.charCodeAt(0) >= 65 && char.charCodeAt(0) <= 90;
const isLowerCase = char => char.charCodeAt(0) >= 97 && char.charCodeAt(0) <= 122;

const flipCase = str => {
    let newStr = '';
    const margin = 32;
    for(let i = 0; i < str.length; i++){
        const curr = str[i];
        if(isLowerCase(curr)){
            newStr += String.fromCharCode(curr.charCodeAt(0) - margin);
        }else if(isUpperCase(curr)){
            newStr += String.fromCharCode(curr.charCodeAt(0) + margin);
        }else{
            newStr += curr;
        };
    };
    return newStr;
};

console.log(flipCase(str));

Output

The output in the console: ?

tHE cASE of ThIS sTRINg wILL bE flIpPED

How It Works

The solution uses ASCII character codes to determine case and perform conversions:

• Uppercase letters (A-Z) have ASCII codes 65-90
• Lowercase letters (a-z) have ASCII codes 97-122
• The difference between uppercase and lowercase is 32
• Non-alphabetic characters remain unchanged

Alternative Method Using Built-in Methods

JavaScript provides simpler built-in methods for case conversion:

const flipCaseSimple = str => {
    return str.split('').map(char => {
        if (char === char.toUpperCase() && char !== char.toLowerCase()) {
            return char.toLowerCase();
        } else if (char === char.toLowerCase() && char !== char.toUpperCase()) {
            return char.toUpperCase();
        }
        return char;
    }).join('');
};

const testStr = 'Hello World! 123';
console.log(flipCaseSimple(testStr));

hELLO wORLD! 123

Conclusion

Case flipping can be achieved using ASCII character codes or built-in string methods. The ASCII approach offers more control, while built-in methods provide cleaner, more readable code.