JSFiddle - React, Tailwind, and code Playground

HTML

<button class="classmonster" onclick="Attack();attackUp();">Attack Mob</button>
<br>
ATK XP <span id="attackxp">0</span>
<br>
i <span id="i">0</span>
<br>
Attack <span id="attack">1</span>

JavaScript

var attackxp = 0;
var attack = 1;

function Attack(){
    var damage = Math.floor(Math.random() * (3+ 1 - 1)) + 1;;
    attackxp = attackxp + (damage * 8);
    document.getElementById('attackxp').innerHTML = attackxp;
 }

var xpforlevel = [83, 174, 276, 388, 512, 650, 801, 969, 1154, 1358, 1584, 1833, 2107, 2411, 2746, 3115, 3523, 3973, 4470, 5018, 5624, 6291, 7028, 7842, 8740, 9730, 10824, 12031, 13363, 14833, 16456, 18247, 20224, 22406, 24815, 27473, 30408, 33648, 37224, 41171, 45529, 50339, 55649, 61512, 67983, 75127, 83014, 91721, 101333, 111945, 123660, 136594, 150872, 166636, 184040, 203254, 224466, 247886, 273742, 302288, 333804, 368599, 407015, 449428, 496254, 547953, 605032, 668051, 737627, 814445, 899257, 992895, 1096278, 1210421, 1336443, 1475581, 1629200, 1798808, 1986068, 2192818, 2421087, 2673114, 2951373, 3258594, 3597792, 3972294, 4385776, 4842295, 5346332, 5902831, 6517253, 7195629, 7944614, 8771558, 9684577, 10692629, 11805606, 13034431];

function attackUp(){
    var i = 0;
    var attackCost = xpforlevel[i];
    if (attackCost < attackxp) {
        alert("WARMING!");
        attack++;                           
   		  document.getElementById('attack').innerHTML = attack;
        i++;
        document.getElementById('i').innerHTML = i;
    }
}