JSFiddle - React, Tailwind, and code Playground

HTML

<div id="rwid1">
			<button id="fighter1Inc">+</button>
			<input type="text" id="fighterScore1" maxlength="10" onkeypress='return event.charCode >= 48 && event.charCode <= 57'>
			<button id="fighter1Dec">-</button>
		</div><!--/rwid-->

JavaScript

var fighterScore1 = document.getElementById("fighterScore1");
fighterScore1.value  = 10;
var fighter1Inc = document.getElementById("fighter1Inc");
var valor = 10;

	fighter1Inc.onclick = function (valor) {
		fighterScore1.value = increaseValue(valor);
	};
	fighter1Dec.onclick = function (valor) {
		fighterScore1.value = decreaseValue(valor);
	};
  function decreaseValue() {
		if (valor <= 0 ) {
valor = 0;
	    } else {
	    valor--;
	    }
	    	return valor;
	};
	function increaseValue() {
		if (valor >= 10 ) {
	    	valor = 10;
	    } else {
	    valor++;
	    }
      return valor;
	    
	};