JSFiddle - React, Tailwind, and code Playground

HTML

<p id="blue"></p>
<p id="red"></p>
<button onclick="startA()">Start for Red</button>
<button onclick="stopA()">Stop for red</button>
<button onclick="startB()">Start for Blue</button>
<button onclick="stopB()">Stop for Blue</button>

JavaScript

var startRed;
var startBlue;
var bluescore = 1;
var redscore = 1;

function startA() {
    stopA();
    startRed = setInterval(function () {
        redscore++;
        updateUI();
    }, 3000)
};

function startB() {
    stopB();
    startBlue = setInterval(function () {
        bluescore++;
        updateUI();
    }, 3000)
};

function stopA() {
    clearInterval(startRed);
};

function stopB() {
    clearInterval(startBlue);
};

function updateUI() {
    document.getElementById("blue").innerHTML = bluescore;
    document.getElementById("red").innerHTML = redscore;
}

updateUI();