js强大的日期格式化函数，不仅可以格式化日期，还可以查询星期，一年中第几天等

/**
* js日期格式化，timestamp支持10位或13位的时间戳，或是时间字符串
* @param{string} format传进来的字符串，Y-m-d H:i:s每个字母所代表的意思详见代码
* @param{int string}timestamp 要格式化的时间 默认为当前时间可以是日期形式的字符串，可以是10位或13位的时间戳
* @return {string} 格式化的时间字符串
*/
function dateFormat(format, timestamp){ 
	if(timestamp=="" || timestamp==null || format=="") return ""

	//如果传进来的是 日期的字符串形式，变回时间戳
	if(typeof(timestamp)=="string"){
	//兼容ios
	var timestamp = timestamp.replace("T"," ")
	if (/(iPhone|iPad|iPod|iOS)/i.test(navigator.userAgent)) { 
	timestamp = timestamp.replace(/\-/g, "/"); 
	}
	if (timestamp.indexOf("-")!==false || timestamp.indexOf("/")!==false ) timestamp = new Date(timestamp).getTime()
	}
	//如果传进来的是10位的时间戳 变成13位的
	if(timestamp.toString().length == 10) timestamp = timestamp * 1000
	//如果到这一步，依然不是13位的时间戳，说明数据有问题
	timestamp = parseInt(timestamp)
	if(timestamp.toString().length != 13) return ""

	var a, jsdate= new Date(timestamp);
	var pad = function(n, c){
	if((n = n + "").length < c){
	return new Array(++c - n.length).join("0") + n;
	} else {
	return n;
	}
	};
	var txt_weekdays = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
	var txt_ordin = {1:"st", 2:"nd", 3:"rd", 21:"st", 22:"nd", 23:"rd", 31:"st"};
	var txt_months = ["", "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]; 
	var f = {
	// Day
	d: function(){return pad(f.j(), 2)},//2位天,02
	D: function(){return f.l().substr(0,3)},//星期单词的前三位
	j: function(){return jsdate.getDate()},//天2
	l: function(){return txt_weekdays[f.w()]},//星期英文
	N: function(){return f.w() + 1},//星期的某一天的数字 星期日为1
	S: function(){return txt_ordin[f.j()] ? txt_ordin[f.j()] : ‘th‘},
	w: function(){return jsdate.getDay()},//星期的某一天的数字 星期日为0
	z: function(){return (jsdate - new Date(jsdate.getFullYear() + "/1/1")) / 864e5 >> 0},//当前时间是一年中的第几天
	// Month
	F: function(){return txt_months[f.n()]},//月份英文
	m: function(){return pad(f.n(), 2)},//2位月02
	M: function(){return f.F().substr(0,3)},//月份英文前三个字母
	n: function(){return jsdate.getMonth() + 1},//月2
	t: function(){ //当前月总共有多少天
	var n;
	if( (n = jsdate.getMonth() + 1) == 2 ){
	return 28 + f.L();
	} else{
	if( n & 1 && n < 8 || !(n & 1) && n > 7 ){
	return 31;
	} else{
	return 30;
	}
	}
	},
	// Year
	L: function(){var y = f.Y();return (!(y & 3) && (y % 1e2 || !(y % 4e2))) ? 1 : 0},	
	//年
	Y: function(){return jsdate.getFullYear()},
	y: function(){return (jsdate.getFullYear() + "").slice(2)},	
	// Time
	a: function(){return getHours(jsdate) > 11 ? "pm" : "am"},
	A: function(){return f.a().toUpperCase()},
	B: function(){
	// peter paul koch:
	var off = (jsdate.getTimezoneOffset() + 60)*60;
	var theSeconds = (getHours(jsdate) * 3600) + (jsdate.getMinutes() * 60) + jsdate.getSeconds() + off;
	var beat = Math.floor(theSeconds/86.4);
	if (beat > 1000) beat -= 1000;
	if (beat < 0) beat += 1000;
	if ((String(beat)).length == 1) beat = "00"+beat;
	if ((String(beat)).length == 2) beat = "0"+beat;
	return beat;
	},
	g: function(){return getHours(jsdate) % 12 || 12},
	G: function(){return getHours(jsdate)},
	h: function(){return pad(f.g(), 2)},
	H: function(){return pad(getHours(jsdate), 2)},
	i: function(){return pad(jsdate.getMinutes(), 2)},
	s: function(){return pad(jsdate.getSeconds(), 2)},
	//u not supported yet
	// Timezone
	//e not supported yet
	//I not supported yet
	O: function(){
	var t = pad(Math.abs(jsdate.getTimezoneOffset()/60*100), 4);
	if (jsdate.getTimezoneOffset() > 0) t = "-" + t; else t = "+" + t;
	return t;
	},
	P: function(){var O = f.O();return (O.substr(0, 3) + ":" + O.substr(3, 2))},
	//T not supported yet
	//Z not supported yet
	// Full Date/Time
	c: function(){return f.Y() + "-" + f.m() + "-" + f.d() + "T" + f.h() + ":" + f.i() + ":" + f.s() + f.P()},
	//r not supported yet
	U: function(){return Math.round(jsdate.getTime()/1000)}
	};
	//兼容ios 
	function getHours(dateObj){
	//因为上边已经将UTC的时间进行了转换，把T去了，所以这里用同样的方法即可
	return dateObj.getHours(); 

	if (/(iPhone|iPad|iPod|iOS)/i.test(navigator.userAgent)) { 
	return dateObj.getUTCHours();
	}else{
	return dateObj.getHours(); 
	}
	} 

	var ret =""
	return format.replace(/[\\]?([a-zA-Z])/g, function(t, s){
	if( t!=s ){
	// escaped
	ret = s;
	} else if( f[s] ){
	// a date function exists
	ret = f[s]();
	} else{
	// nothing special
	ret = s;
	}
	return ret;
	});
}

//年月日时分秒
var temp = dateFormat("Y-m-d H:i:s",new Date().getTime());
console.log(temp);
//月日
var temp = dateFormat("m-d","2018-02-24");
console.log(temp);
//星期月份
var temp = dateFormat("F","2018-02-24");
console.log(temp);
//星期英文
var temp = dateFormat("l","2018-02-24");
console.log(temp);
//一周中的第几天，周日为第一天
var temp = dateFormat("N","2018-02-24");
console.log(temp);
//一周中的第几天，周一为第一天
var temp = dateFormat("w","2018-02-24");
console.log(temp);
//一年中的第几天
var temp = dateFormat("z","2018-02-24");
console.log(temp);
//获取某个日期在这一年的第几周   Math.ceil(一年中第几天 / 7)
var temp = Math.ceil( dateFormat("z","2018-03-10") / 7)
console.log(temp);
//获取某月有多少天
var temp = dateFormat("t","2018-02-24");
console.log(temp);