get week nr

by djwave28

HTML

<div id="display"></div>

JavaScript

// function to insert into html
function insert(str) {
    var display = document.getElementById("display");
    var node = document.createTextNode(str);
    display.appendChild(node);
    var p = document.createElement("p");
    display.appendChild(p);

}

// new Date(year, month[, day[, hour[, minutes[, seconds[, milliseconds]]]]]);

var now = new Date();

// set an offset in days. Add days to see the week change.
var offset = 0;
var testday = new Date(now.getTime() + offset * 24 * 60 * 60 * 1000);
insert("Testdate: " + testday);

var firstofyear = new Date(testday.getFullYear(), 0, 1);
insert("firstofyear: " + firstofyear);


var firstdayoffset = firstofyear.getDay();
insert("firstdayoffyear offset: " + firstdayoffset);



var daynr = Math.ceil((testday - firstofyear) / 86400000);
insert("current daynr:" + daynr);

var realday = daynr - firstdayoffset;
var str = "Do some math: current - firstdayoffyear = " + realday;
insert(str);


var weeknr = (daynr - firstdayoffset) / 7;
insert("weeknr: Math.ceil(" + realday + "/7) + 1 = " + parseInt(Math.ceil(weeknr) + 1));