let date = new Date(2019, 0, 1);
document.write('기준일자 : ' + date + '<br>');

date.setHours(date.getHours() + 10);
document.write('10시간 후 : ' + date + '<br>');

date = new Date(2019, 0, 1);
date.setHours(date.getHours() - 10);
document.write('10시간 전 : ' + date + '<br>');


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