javascript Date.prototype

Date.prototype.format = function(format){
var o = {
"M+" : this.getMonth()+1, //month
"d+" : this.getDate(), //day
"h+" : this.getHours(), //hour
"m+" : this.getMinutes(), //minute
"s+" : this.getSeconds(), //second
"q+" : Math.floor((this.getMonth()+3)/3), //quarter
"S" : this.getMilliseconds() //millisecond
};
if(/(y+)/.test(format)) {
format = format.replace(RegExp.$1, (this.getFullYear()+"").substr(4 - RegExp.$1.length));
}
for(var k in o) {
if(new RegExp("("+ k +")").test(format)) {
format = format.replace(RegExp.$1, RegExp.$1.length==1 ? o[k] : ("00"+ o[k]).substr((""+ o[k]).length));
}
}
return format;
};

// `getDayOfYear` returns the day number for the year
Date.prototype.getDayOfYear = function () {
var fd = new Date(this.getFullYear(), 0, 0);
var sd = new Date(this.getFullYear(), this.getMonth(), this.getDate());
return Math.ceil((sd - fd) / 86400000);
};

// `getWeekOfYear` returns the week number for the year
Date.prototype.getWeekOfYear = function () {
var ys = new Date(this.getFullYear(), 0, 1);
var sd = new Date(this.getFullYear(), this.getMonth(), this.getDate());
if (ys.getDay() > 3) {
ys = new Date(sd.getFullYear(), 0, (7 - ys.getDay()));
}
var daysCount = sd.getDayOfYear() - ys.getDayOfYear();
return Math.ceil(daysCount / 7);

};

// `getDaysInMonth` returns the number of days in a month
Date.prototype.getDaysInMonth = function () {
return 32 - new Date(this.getFullYear(), this.getMonth(), 32).getDate();
};

// `hasWeek` returns `true` if the date resides on a week boundary
// **????????????????? Don't know if this is true**
Date.prototype.hasWeek = function () {
var df = new Date(this.valueOf());
df.setDate(df.getDate() - df.getDay());
var dt = new Date(this.valueOf());
dt.setDate(dt.getDate() + (6 - dt.getDay()));

if (df.getMonth() === dt.getMonth()) {
return true;
} else {
return (df.getMonth() === this.getMonth() && dt.getDate() < 4) || (df.getMonth() !== this.getMonth() && dt.getDate() >= 4);
}
};

// `getDayForWeek` returns the Date object for the starting date of
// the week # for the year
Date.prototype.getDayForWeek = function () {
var df = new Date(this.valueOf());
df.setDate(df.getDate() - df.getDay());
var dt = new Date(this.valueOf());
dt.setDate(dt.getDate() + (6 - dt.getDay()));
if ((df.getMonth() === dt.getMonth()) || (df.getMonth() !== dt.getMonth() && dt.getDate() >= 4)) {
return new Date(dt.setDate(dt.getDate() - 3));
} else {
return new Date(df.setDate(df.getDate() + 3));
}
};

// `getWeekId` returns a string in the form of 'dh-YYYY-WW', where WW is
// the week # for the year.
// It is used to add an id to the week divs
Date.prototype.getWeekId = function () {
var y = this.getFullYear();
var w = this.getDayForWeek().getWeekOfYear();
var m = this.getMonth();
if (m === 11 && w === 1) {
y++;
}
return 'dh-' + y + "-" + w;
};