function countdown_function(){
	const now = new Date();  //今の日時
	const target = new Date(now.getFullYear(), now.getMonth(), now.getDate(), '23','59','59');
	const targetMonth = now.getYear();
	const targetDate = now.getDate();
	const remainTime = target - now  //差分を取る（ミリ秒で返ってくる
    
    //指定の日時を過ぎていたら処理をしない
    if(remainTime < 0) return false 

    //差分の日・時・分・秒を取得
    const difDay  = Math.floor(remainTime / 1000 / 60 / 60 / 24)
    const difHour = Math.floor(remainTime / 1000 / 60 / 60 ) % 24
    const difMin  = Math.floor(remainTime / 1000 / 60) % 60
    const difSec  = Math.floor(remainTime / 1000) % 60

    //残りの日時を上書き    
    let elements;
    elements = document.getElementsByClassName("countdown-day");
    Array.prototype.forEach.call( elements , e => e.textContent = difDay );
    
    elements = document.getElementsByClassName("countdown-hour");
    Array.prototype.forEach.call( elements , e => e.textContent = difHour );
    
    elements = document.getElementsByClassName("countdown-min");
    Array.prototype.forEach.call( elements , e => e.textContent = difMin );
    
    elements = document.getElementsByClassName("countdown-sec");
    Array.prototype.forEach.call( elements , e => e.textContent = difSec );
    
    elements = document.getElementsByClassName("limit-month");
    Array.prototype.forEach.call( elements , e => e.textContent = targetMonth );
    
    elements = document.getElementsByClassName("limit-date");
    Array.prototype.forEach.call( elements , e => e.textContent = targetDate );

    //指定の日時になればカウントを止める
    if(remainTime < 0) clearInterval(countdown)
}

let countdown = setInterval(function(){countdown_function()}, 1000);	//1秒間に1度処理