Thanks, I finally solved this question myself

function strReplace() {
        var text_input = $('#text-input').val();
        var text_split = text_input.split(' ');
        var word;
        var str;
        var final = [];
        String.prototype.allReplace = function(obj) {
            var retStr = this;
            for (var x in obj) {
                retStr = retStr.replace(new RegExp(x, 'g'), obj[x]);
            }
            return retStr;
        };
        for (var i = 0; i < text_split.length; i++) {
            word = text_split[i].split('');
            for (var x = 0; x < 3; x++) {
                if (
                    word[x] === 'о' ||
                    word[x] === 'р' ||
                    word[x] === 'с' ||
                    word[x] === 'а' ||
                    word[x] === 'у' ||
                    word[x] === 'е' ||
                    word[x] === 'О' ||
                    word[x] === 'Р' ||
                    word[x] === 'С' ||
                    word[x] === 'А' ||
                    word[x] === 'К' ||
                    word[x] === 'Е' ||
                    word[x] === 'Т' ||
                    word[x] === 'Х' ||
                    word[x] === 'М' ||
                    word[x] === 'Н' ||
                    word[x] === '3' ||
                    word[x] === '0' ||
                    word[x] === '1'
                ) {
                    word[x] = word[x].allReplace({
                        'о': 'o',
                        'р': 'p',
                        'с': 'c',
                        'а': 'a',
                        'у': 'y',
                        'е': 'e',
                        'О': 'O',
                        'Р': 'P',
                        'С': 'C',
                        'А': 'A',
                        'К': 'K',
                        'Е': 'E',
                        'Т': 'T',
                        'Х': 'X',
                        'М': 'M',
                        'Н': 'H',
                        '3': 'З',
                        '0': 'O',
                        '1': 'l'
                    });
                }
            }
            str = word;
            str = str.join('');
            str = str.concat(' ');
            final += str + "";
        }
        console.log(final);

        document.getElementById("text-output").innerHTML = final;
        $('.btn-copy').attr('data-clipboard-text', final);
    }

I want to change not greater than 3 symbols in word, but I have string, which I split. Have you answer for me? (Maybe sorry for my English)

function strReplace() {
  var text_input = $('#text-input').val();
  var text_split = text_input.split(' ');
  String.prototype.allReplace = function(obj) {
    var retStr = this;
    for (var x in obj) {
      retStr = retStr.replace(new RegExp(x, 'g'), obj[x]);
    }
    return retStr;
  };

  for (var i = 0; i < text_split.length; i++) {
    text_split[i] = text_split[i].allReplace({
      'о': 'o',
      'р': 'p',
      'с': 'c',
      'а': 'a',
      'у': 'y',
      'е': 'e',
      'О': 'O',
      'Р': 'P',
      'С': 'C',
      'А': 'A',
      'К': 'K',
      'Е': 'E',
      'Т': 'T',
      'Х': 'X',
      'М': 'M',
      'Н': 'H',
      '3': 'З',
      '0': 'O',
      '1': 'l'
    });
  }
  document.getElementById("text-output").innerHTML = text_split.join(' ');
  $('.btn-copy').attr('data-clipboard-text', text_split.join(' '));
}