CIS 119 Date formatter

Source code

function pad(str, cols, ch) {
    while ((""+str).length < cols) str = ch + str;
    return str;
}

function displayTime() {
    var militaryformat = false;
    if (document.getElementById("miltime").checked) {
        militaryformat = true;
    }
    var now = new Date();
    var hours = now.getHours();
    var ampm = "";
    if (!militaryformat) {
        if (hours >= 12) ampm = " pm";
        else ampm = " am";
        if (hours == 0) hours = 12;
        else if (hours > 12) hours -= 12;
    }
    document.getElementById("clock").value = hours
        + ':' + pad(now.getMinutes(), 2, '0') + ':'
        + pad(now.getSeconds(), 2, '0') + ampm;
}

window.onload = function() {
    displayTime();
    var timer = setInterval(displayTime, 1000);
    document.getElementById('btnStop').onclick = function() {
        var btn = document.getElementById('btnStop');
        if (btn.value == "Stop clock") {
            clearInterval(timer);
            btn.value = "Start clock";
        } else {
            displayTime();
            btn.value = "Stop clock";
            timer = setInterval(displayTime, 1000);
        };
    };
};