app.js

const durationInput = document.querySelector('#duration');
const startButton = document.querySelector('#start');
const pauseButton = document.querySelector('#pause');
const circle = document.querySelector('circle');
const perimeter = circle.getAttribute('r') * 2 * Math.PI;
circle.setAttribute('stroke-dasharray', perimeter); // <circle stroke-dasharrar="perimeter"></circle>

let duration;
const timer = new Timer(durationInput,startButton,pauseButton,{
    onStart(totalDuration){
        duration = totalDuration;
    },

    onTick(timeRemaining){
        circle.setAttribute('stroke-dashoffset', 
        perimeter * timeRemaining / duration - perimeter
        );
        
    }
});