Duplicate Encoder for string

duplicateEncodeString.js

//original
function duplicateEncode(word) {

    let result = '';
    let textHash = {};

    for (let i = 0; i < word.length; i++) {

        let key = word.charAt(i).toLowerCase();

        switch (textHash[key]) {
            case true:
                textHash[key] = false;
                break;
            case false:
                break;
            default:
                textHash[key] = true;
        }
    }

    for (i = 0; i < word.length; i++) {

        key = word.charAt(i).toLowerCase();

        if (textHash[key]) {
            result = result + 'Uni';
        } else {
            result = result + 'Dup';
        }
    }

    console.log(textHash);

    return result;
}

//best
function duplicateEncode(word){
  return word
    .toLowerCase()
    .split('')
    .map( function (currentValue, index, array) {
      return array.indexOf(currentValue) == array.lastIndexOf(currentValue) ? 'Uni' : 'Dup'
    })
    .join('');
}

//fork
function duplicateEncode(word){
  return []
    .map
    .call(word.toLowerCase(), function (a, i, w) {
      return w.indexOf(a) == w.lastIndexOf(a) ? '(' : ')'
    })
    .join('');
}