getDays()函数接收哪月值和哪年值，并且建立一个有12个元素的数组，用来存放每月的天数，哪一年用来决定是不是闰年，在闰年中二月是29天，而不是闰年是28天。该函数返回指定月份的天数。

以下是getDays()：

function getDays(month, year) {
// create array to hold number of days in each month
var ar = new Array(12);
ar[0] = 31; // January
ar[1] = (leapYear(year)) ? 29 : 28; // February
ar[2] = 31; // March
ar[3] = 30; // April
ar[4] = 31; // May
ar[5] = 30; // June
ar[6] = 31; // July
ar[7] = 31; // August
ar[8] = 30; // September
ar[9] = 31; // October
ar[10] = 30; // November
ar[11] = 31; // December

// return number of days in the specified month (parameter)
return ar[month];
}

如果指定的年数可以被4整除，那么leapYear()函数将返回“true”，否则返回”false“：

function leapYear(year) {
if (year % 4 == 0) // basic rule
return true; // is leap year
/* else */ // else not needed when statement is "return"
return false; // is not leap year
}
getMonthName()函数返回指定月份的名字：
function getMonthName(month) {
// create array to hold name of each month
var ar = new Array(12);
ar[0] = "January";
ar[1] = "February";
ar[2] = "March";
ar[3] = "April";
ar[4] = "May";
ar[5] = "June";
ar[6] = "July";
ar[7] = "August";
ar[8] = "September";
ar[9] = "October";
ar[10] = "November";
ar[11] = "December";

// return name of specified month (parameter)
return ar[month];
}

setCal()函数是主模块，我们在脚本的第一行调用它。该函数为当天（now）、和每月的第一天（firstDayInstance）建立一个Date对象。用这些对象，setCal()函数解析出关于一个月的第一天、当日，和最后一天的所有信息。

function setCal() {
// standard time attributes
var now = new Date();
var year = now.getFullYear();
var month = now.getMonth();
var monthName = getMonthName(month);
var date = now.getDate();
now = null;

// create instance of first day of month, and extract the day on which it occurs
var firstDayInstance = new Date(year, month, 1);
var firstDay = firstDayInstance.getDay();
firstDayInstance = null;

// number of days in current month
var days = getDays(month, year);

// call function to draw calendar
drawCal(firstDay + 1, days, date, monthName, year);
}