main.js

let timeseconds=10;
const timer = document.getElementById('countdown_clock');
var CountDown;

    // Pause or continue the Countdown Clock

let btn = document.getElementById("play"); 
var clicked = false;

function toggle() {
    if (clicked == false) {
        clicked=true
        btn.innerHTML="Pause"

        clearInterval(CountDown);
        
        //countdown our timer
        CountDown = setInterval (()=>{
            timeseconds--;
            DisplayTime(timeseconds);
            if(timeseconds <=0 || timeseconds<1){
                clearInterval(CountDown);
            }  
            
        },1000);

        function DisplayTime(second) {
            const min = Math.floor(second / 60);
            const sec = Math.floor(second % 60);

            timer.innerHTML = `
            ${min < 10 ? "0" : ""}${min}:${sec < 10 ? "0" : ""}${sec}
            `;
        };
    } else {
        clicked=false;
        btn.innerHTML="Play";
        if(timeseconds <=0 || timeseconds<1){
            clearInterval(CountDown);
        }  
    }
}