JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" id="start" value="Start" />
<div id="output"></div>

JavaScript

var SIMULATIONS = 10000;

var TURNS = 5; // Number of flies to pass by
var MAX = 3; // Number of flies to get full
var
CATCH = 0.5; // Probability to catch fly
var total = 0; // Times simulation was run
var wins = 0; // Times spider got full


var btnStart = document.getElementById("start");
var btnStop = document.getElementById("stop");
var output = document.getElementById("output");
var history = document.getElementById("history");
btnStart.addEventListener('click', start);
btnStart.addEventListener('click', start);


function simulate() {
    deaths = 0;
    total++;
    for (var i = 1; i <= TURNS; i++) {
        if (Math.random() >
        CATCH) {
            deaths++;
            if (deaths == MAX) {
                wins++;
                break;
            }
        }
    }
}

function start() {
    var runs = SIMULATIONS;
    while (runs-- > 0) {
        simulate();
    }
    update();
}

function status() {
    var percent = Math.round(100 * wins / total) / 100;
    return percent + "% (" + wins + " / " + total + ")";
}

function update() {
    var stats = status();
    output.innerHTML = stats;
}