myDate.getThisMonth();
myDate.getThreeMonth();
myDate.getThisYear();

调用可以获取本月，近三个月，今年的日期 * @param obj * @constructor */ function DateHelp(obj) { /*var obj = { date:'2015-02-01',//从此日期开始计算 type:'month',//以年月日向前计算：年（year），月（month），日（day） value:'14',//向前计算的数值，年月日 format:'yyyy/mm/dd'//日期格式 }*/

this.date = obj.date;
this.type = obj.type;
this.value = obj.value == undefined ? obj.value : 0;
this.format = obj.format == undefined ? obj.format: 'yyyy/MM/dd';

//日期和非日期格式获取年月日
if (this.date instanceof Date){
//处理传进来的是日期函数的

this.year = this.date.getFullYear();
this.month = this.date.getMonth()+1;
this.day = this.date.getDate();
}else{
//处理传入的是非日期函数的

this.year = this.date.substr(0,4);
this.month = this.date.substr(5,2);
this.day = this.date.substr(8,2);
}

}

DateHelp.prototype.beforeDate = function(type,value){

var _type = type || this.type,_value = value || this.value,_year = this.year,_month = this.month,_day = this.day;

if (_type == 'year' || _type == '年'){
_year -= _value;
}else if (_type == 'month' || _type == '月'){
_year -= parseInt(_value / 12);
_month -= _value % 12;
if(_month <= 0){
_year -= 1;
_month += 12;
}
}else if (_type == 'day' || _type == '日'){

}else {

}

var date = new Date(_year,_month - 1,_day)
return this.formatDate(date,this.format);
}

DateHelp.prototype.formatDate = function(date,fmt){

var o = {
"M+" : date.getMonth()+1,//月份
"d+" : date.getDate(),//日
"h+" : date.getHours(),//小时
"m+" : date.getMinutes(),//分
"s+" : date.getSeconds(),//秒
"q+" : Math.floor((date.getMonth()+3)/3),//季度
"S" : date.getMilliseconds() //毫秒
};
if(/(y+)/.test(fmt))
fmt=fmt.replace(RegExp.$1,(date.getFullYear()+"").substr(4 - RegExp.$1.length));
for(var k in o)
if(new RegExp("("+ k +")").test(fmt))
fmt = fmt.replace(RegExp.$1,(RegExp.$1.length==1) ? (o[k]) : (("00"+ o[k]).substr((""+ o[k]).length)));
return fmt;
}

DateHelp.prototype.getThisMonth = function() {

var first = new Date(this.year,this.month - 1);
var last = new Date(this.year,this.month,0);

return this.formatDate(first,this.format) + " - " + this.formatDate(last,this.format);
}

DateHelp.prototype.getThreeMonth = function() {

return this.beforeDate('month',3) + " - " + this.beforeDate('day',0);
}

DateHelp.prototype.getThisYear = function() {

var first = new Date(this.year,1);
var last = new Date(this.year,11,31);

return this.formatDate(first,this.format);
}

/*
//示例
var myDate = new DateHelp({
date:'2015-02-01',//从此日期开始计算
format:'yyyy/MM/dd'
});

console.log(myDate.getThisMonth());
console.log(myDate.getThreeMonth());
console.log(myDate.getThisYear());*/

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