CIS 119 Display calendar

Source code

var win = null;
var month = new Array('January', 'February', 'March',
    'April', 'May', 'June', 'July', 'August', 'September',
    'October', 'November', 'December');

function $(id) { return document.getElementById(id); }

function displayCal() {
    var f = $('frm1');
    if (win == null || win.closed) {
        win = window.open("", "cal", "width=320,height=280");
    }

    var days = new Array('Sun', 'Mon', 'Tue', 'Wed',
        'Thu', 'Fri', 'Sat');
    var ctr;

    for (ctr=0; ctr<12; ctr++) {
        if (f.lstMonth[ctr].selected) break;
    }
    var dx = new Date();
    if (ctr >= 12) ctr = dx.getMonth();
    if (f.yr.value < 1900 || f.yr.value > 3999) f.yr.value = dx.getFullYear();
    var d0 = new Date(f.yr.value, ctr, 1);
    var dx = new Date(d0.getFullYear(), ctr, 1);

    win.document.writeln('<table align="center" border="1">');
    win.document.writeln('<caption align="top"><h3>' +
        month[d0.getMonth()] + ' ' + d0.getFullYear() +
        '</h3></caption>');
    win.document.write('<tr>');
    for (ctr=0; ctr<7; ctr++) {
        win.document.write('<th width="14%">' + days[ctr] + '</th>');
    }
    win.document.writeln('</tr>');

    ctr = d0.getDay();
    if (ctr > 0) {
        win.document.write('<tr align="right">');
        while (ctr-- > 0) {
            win.document.write('<td> </td>');
        }
    }
    while (d0.getMonth() == dx.getMonth()) {
        if (d0.getDay() == 0) {
            win.document.write('<tr align="right">');
        }
        var d = d0.getDate();
        win.document.write('<td>' + d + '</td>');
        if (d0.getDay() == 6) {
            win.document.writeln('</tr>');
        }
        d0.setDate(d0.getDate() + 1);
    }

    if (d0.getDay() != 0) {
        ctr = 7 - d0.getDay();
        while (ctr-- > 0) {
            win.document.write('<td> </td>');
        }
        win.document.writeln('</tr>');
    }

    win.document.writeln('</table>');
    win.document.close();
    return false;
}

function init() {
    $("frm1").onsubmit = function() { return false; }
    $("submitButton").onclick = displayCal;
    var d = new Date();
    for (var i=0; i<12; i++) $("lstMonth").options[i] = new Option(month[i]);
    $("lstMonth").selectedIndex = d.getMonth();
    $("yr").value = d.getFullYear();
}

window.onload = init;