JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="texto"/>

CSS

#texto{float:left;}
#contador{float:left;clear:both;}

JavaScript

jQuery.fn.repeticiones = function(){
    
    function substr_count (haystack, needle, offset, length) {
  // http://kevin.vanzonneveld.net
  // +   original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +   bugfixed by: Onno Marsman
  // +   improved by: Brett Zamir (http://brett-zamir.me)
  // +   improved by: Thomas
  // *     example 1: substr_count('Kevin van Zonneveld', 'e');
  // *     returns 1: 3
  // *     example 2: substr_count('Kevin van Zonneveld', 'K', 1);
  // *     returns 2: 0
  // *     example 3: substr_count('Kevin van Zonneveld', 'Z', 0, 10);
  // *     returns 3: false

  var cnt = 0;

  haystack += '';
  needle += '';
  if (isNaN(offset)) {
    offset = 0;
  }
  if (isNaN(length)) {
    length = 0;
  }
  if (needle.length == 0) {
    return false;
  }
  offset--;

  while ((offset = haystack.indexOf(needle, offset + 1)) != -1) {
    if (length > 0 && (offset + needle.length) > length) {
      return false;
    }
    cnt++;
  }

  return cnt;
}


$(this).each(function(){
	var input = $(this);
	var contador = $("<span id='contador'></span>");
	input.after(contador);

	input.keyup(function(e){
		input = $(this);
		var clave = input.attr('value');

		function repCarac(p){
			var carac, expr;
			var coinc;
			var coincacum = '';
			var numcoinc = 0;
			for(var i=0;i<p.length;i++){
				carac = p.charAt(i);
                coinc = substr_count(p, carac);
                if (coinc > 1) {
                    if (substr_count(coincacum, carac)) continue;
                    else {
                        coincacum = coincacum + carac;
						numcoinc = numcoinc + coinc;
                    }
                }
				/*expr = new RegExp(carac,'g');
				coinc = p.match(expr);
				if(coinc.length > 1){
					if(coincacum.match(expr))
						{continue;}
					else{
						coincacum = coincacum + carac;
						numcoinc = numcoinc + coinc.length;
					}
				}*/
			}
			return numcoinc;
		}
		contador.text('coincidencias:...