下記のスクリプトを実行しましたので
Consoleで結果を確認できます。
function isHoliday(date) { const req = new XMLHttpRequest(); req.open('get', 'syukujitsu.csv', true); req.send(null); req.onload = function() { checkDate(req.responseText, date, function(result) { console.log(date, result); }); }; } function checkDate(str, date, callback) { const data = []; const nDate = new Date(date); let dataArr = []; let checkDate = nDate.getFullYear() + '/' + (nDate.getMonth() + 1) + '/' + nDate.getDate(); let isHoliday = false; let tmp = str.split('\n'); for (let i=0; i< tmp.length; i++) { dataArr = tmp[i].split(','); if (dataArr[0] === checkDate) { isHoliday = true; break; } }; callback(isHoliday); } isHoliday('2018-01-01'); // => 2018-01-01 true isHoliday('2018-01-02'); // => 2018-01-02 false isHoliday('2018/08/05 12:34'); // => 2018/08/05 12:34 false isHoliday('2019-05-05 00:00:00'); // => 2019-05-05 00:00:00 true