Query.js

var mysql = require('mysql');

// Create Pool membutuhkan koneksi internet
var pool = mysql.createPool({
	host: 'localhost',
	user: 'root',
	password: '',
	database: 'test_pulsa',
});

module.exports = {
	getID: function(table, id_code, ymd_dates, column_id, total_additional_digit){
		var query = "SELECT * FROM "+table+" ORDER BY "+column_id+" DESC LIMIT 1";

		pool.getConnection(function(err, connection){
			connection.query(query, function(error, result, fields){
				connection.release();

				return new Promise((resolve, reject) => {
					if(error){
						console.log(error);
					} else {
						var new_id;
						if(result.length == 0){
							var pad = "";
							for(var i=1; i<total_additional_digit; i++){
								pad += "0";
							}
							var new_id = id_code+ymd_dates+pad+1;

						} else {
							var last_id = result[0][column_id];
							var last_id_date = last_id.substr(id_code.length, (id_code.length+ymd_dates.length)-1);

							if(last_id_date != ymd_dates){
								var pad = "";
								for(var i=1; i<total_additional_digit; i++){
									pad += "0";
								}
								var new_id = id_code+ymd_dates+pad+1;

							} else {
								var last_additional_digit = parseInt(last_id.substr((id_code+ymd_dates).length));
								var new_additional_digit = (last_additional_digit+1).toString();
								var pad = "";
								for(var i=0; i<total_additional_digit; i++){
									pad += "0";
								}
								new_additional_digit = (pad+new_additional_digit).substr(new_additional_digit.length);
								var new_id = id_code+ymd_dates+new_additional_digit;

							}
						}

						console.log(new_id); // Hasilnya muncul di console
						resolve(new_id); // Hasilnya undefined di router
					}
				})
			})
		})
	}
}