CyberCoded - Articles

Articles | Monday's child is full of grace | back

Introduction
Days of the Week
Calculating the day of the week
Converting it to a named day
Monday's Child
The whole date and nothing but the date
Working Example
Source Code

Introduction

This article will demonstrate how to calculate the day of the week of any date.

Using this information we will retrieve the relevant line from "Monday's Child":

Monday's child is fair of face,
Tuesday's child is full of grace,
Wednesday's child is full of woe,
Thursday's child has far to go,
Friday's child is loving and giving,
Saturday's child works hard for a living,
And the child that is born on the Sabbath day
Is bonny and blithe and good and gay.

It will also describe how to display the full information for the date given, e.g. Tuesday 28th October 1997.

Days of the Week

The following piece of code creates two arrays daysofweek[] and child[] using the makeArray() function as described in the previous article Blind Date.

function makeArray()    {
    this[0] = makeArray.arguments.length;
    for (i = 0; i<makeArray.arguments.length; i++)
        this[i+1] = makeArray.arguments[i];
}

var daysofweek = new makeArray('Sunday',
                               'Monday',
                               'Tuesday',
                               'Wednesday',
                               'Thursday',
                               'Friday',
                               'Saturday');

var child      = new makeArray('is bonny and blithe

                                and good and gay',
                               'is full of grace',
                               'is fair of face',
                               'is full of woe',
                               'has far to go',
                               'is loving and giving',
                               'works hard for a living');

Calculating the day of the week

The following was taken from The Calendar FAQ at http://www.tondering.dk/claus/calendar.html

To calculate the day on which a particular date falls, the following algorithm may be used (the divisions are integer divisions, in which the remainders are discarded):

a = (14 - month) / 12
y = year - a
m = month + 12*a - 2
d = (day + y + y/4 - y/100 + y/400 + (31*m/12) % 7

The value of d is 0 for a Sunday, 1 for a Monday, 2 for a Tuesday, etc.

This can be converted into the following simple script, where Math.floor converts floating point numbers to integers:

function DayOfWeek(day,month,year) {
    var a = Math.floor((14 - month)/12);
    var y = year - a;
    var m = month + 12*a - 2;
    var d = (day + y + Math.floor(y/4) - Math.floor(y/100) +
             Math.floor(y/400) + Math.floor((31*m)/12)) % 7;
    return d;
}

Converting it to a named day

To test the function out, we'll find the day of the week that I was born on, by using the daysofweek[] array to display the day name:

document.write(daysofweek[DayOfWeek(4,1,1965) + 1]);

Which when run produces the following:

Monday

However, rather than remember to have to add 1 to the result each time, it would be better to recode the DayOfWeek() function as:

function DayOfWeek(day,month,year) {
    var a = Math.floor((14 - month)/12);
    var y = year - a;
    var m = month + 12*a - 2;
    var d = (day + y + Math.floor(y/4) - Math.floor(y/100) +
             Math.floor(y/400) + Math.floor((31*m)/12)) % 7;
    return d + 1;
}

Now we would use the following to find out the day of the week of Christmas Day 1900:

document.write(daysofweek[DayOfWeek(25,12,1900)]);

Which when run produces the following:

Tuesday

Monday's Child

Now that we have the integer that refers to the day of the week, we can used the child[] array created earlier to show the relevant line from "Monday's Child" using the following Child() function:

function Child(dayofweek) {
    return daysofweek[dayofweek] + '\'s child ' + child[dayofweek];
}

document.write(Child(DayOfWeek(25,12,1900)));

Which when run produces:

Tuesday's child is fair of face

The whole date and nothing but the date

With the addition of the monthsofyear[] array and the following two functions Nths() and FullDate() we can show the full information for a given date, e.g. Tuesday 28th October 1997.

var monthsofyear = new makeArray('January',
                                 'February',
                                 'March',
                                 'April',
                                 'May',
                                 'June',
                                 'July',
                                 'August',
                                 'September',
                                 'October',
                                 'November',
                                 'December');

function Nths(day) { 
    if (day == 1 || day == 21 || day == 31) return 'st';
    if (day == 2 || day == 22) return 'nd';
    if (day == 3 || day == 23) return 'rd';
    return 'th';
}

function FullDate(day,month,year) {
    return daysofweek[DayOfWeek(day,month,year)] +' '+ day + Nths(day) +