ドットインストール - 3分動画でマスターできるプログラミング学習サービス

main.js

'use strict';

{
    const timer = document.getElementById('timer');
    const start = document.getElementById('start');
    const stop = document.getElementById('stop');
    const reset = document.getElementById('reset');

    let startTime;

    function countUp(){
        // console.log(Date.now() - startTime);
        const d = new Date(Date.now() - startTime);
        const m = String(d.getMinutes()).padStart(2, '0');
        const s = String(d.getSeconds()).padStart(2, '0');
        const ms = String(d.getMilliseconds()).padStart(3, '0');
        timer.textContent = `${m}:${s}.${ms}`;
        console.log(`${m}:${s}.${ms}`);


        setTimeout(() =>{
            countUp();
        }, 10);
    }

    start.addEventListener('click', () =>{
        startTime = Date.now();
        countUp();
    });
}