text-swap-case/dist.es2015/index.js

Convert a text by swapping every character from upper to lower case, or lower to upper case

export function swapCase(input) {
    if (!input)
        return "";
    let result = "";
    for (let i = 0; i < input.length; i++) {
        const lower = input[i].toLowerCase();
        result += input[i] === lower ? input[i].toUpperCase() : lower;
    }
    return result;
}