Letters Combinations

function lettersCombination(input) {
    let x = input[0].charCodeAt(0);
    let y = input[1].charCodeAt(0);
    let z = input[2].charCodeAt(0);
    let counter = 0;
    let output = '';

    for (let i = x; i <= y; i++) {
        for (let k = x; k <= y; k++) {
            for (let j = x; j <= y; j++) {
                if (i !== z && k !== z && j !== z) {
                    output += String.fromCharCode(i) + String.fromCharCode(k) + String.fromCharCode(j) + ' ';
                    counter++;
                }
            }
        }
    }
    console.log(output + counter);
}