计算本年 本月 本周的起始日期

html:

<table><tr><td align="right" width="120px">
销售时间区间:</td><td><select id="ddlChoiceDate" name="ddlChoiceDate" runat="server" onchange="SelectChange(this.value);"><option value="选择时间" selected>选择时间</option><option value="今天">今天</option><option value="本周">本周</option><option value="本月">本月</option><option value="今年">今年</option></select></td><td align="left"><input type="text" id="txtOrd_CreateTimeStart" runat="server" width="85px" onfocus="DateTimeStart(this,'txtOrd_CreateTimeEnd');"disabled="" />
至
<input type="text" id="txtOrd_CreateTimeEnd" runat="server" width="85px" onfocus="DateTimeEnd(this,'txtOrd_CreateTimeStart');"disabled="" /></td></tr></table>

 js:

js: 
<script>//根据销售时间区间下拉列表框的选择判断时间截止文本框是否可用
function TxtDisabled() {if ($("#ddlChoiceDate").val() == "选择时间") {$("#txtOrd_CreateTimeStart").removeAttr("disabled"); //可用
$("#txtOrd_CreateTimeEnd").removeAttr("disabled"); //可用
} else {$("#txtOrd_CreateTimeStart").attr("disabled", "disabled"); //禁用
$("#txtOrd_CreateTimeEnd").attr("disabled", "disabled"); //禁用
}}$(document).ready(function () {TxtDisabled();});function SelectChange(selVal) {TxtDisabled();switch (selVal) {case "选择时间":$("#txtOrd_CreateTimeStart").val(""); //txtOrd_CreateTimeStart
 $("#txtOrd_CreateTimeEnd").val(""); //txtOrd_CreateTimeEndbreak;case "今天":$("#txtOrd_CreateTimeStart").val(getThisDayTime("txtOrd_CreateTimeStart")); //txtOrd_CreateTimeStart
 $("#txtOrd_CreateTimeEnd").val(getThisDayTime("txtOrd_CreateTimeEnd")); //txtOrd_CreateTimeEndbreak;case "本周":$("#txtOrd_CreateTimeStart").val(getWeekTime("txtOrd_CreateTimeStart")); //txtOrd_CreateTimeStart
 $("#txtOrd_CreateTimeEnd").val(getWeekTime("txtOrd_CreateTimeEnd")); //txtOrd_CreateTimeEndbreak;case "本月":$("#txtOrd_CreateTimeStart").val(getMonthTime("txtOrd_CreateTimeStart")); //txtOrd_CreateTimeStart
 $("#txtOrd_CreateTimeEnd").val(getMonthTime("txtOrd_CreateTimeEnd")); //txtOrd_CreateTimeEndbreak;case "今年":$("#txtOrd_CreateTimeStart").val(getYearTime("txtOrd_CreateTimeStart")); //txtOrd_CreateTimeStart
 $("#txtOrd_CreateTimeEnd").val(getYearTime("txtOrd_CreateTimeEnd")); //txtOrd_CreateTimeEndbreak;default:break;}}var now = new Date();//获取当前时间
var Year = now.getFullYear();//得到年
var Month = now.getMonth() + 1; //得到月 //getMonth()是以0开始的月份 //当前月值（1月=0，12月=11）
var Day = now.getDate(); //得到日
var GDay = now.getDay();//得到星期几 0:星期日 1:星期一 2:星期二 3:星期三 4:星期四 5:星期五 6:星期六
function getThisDayTime(id) {var beginTime = "";if (Day < 10) {beginTime = Year + "-" + Month + "-0" + Day; //格式 Y-m-d
 } else {beginTime = Year + "-" + Month + "-" + Day; //格式 Y-m-d
 }return beginTime;}//计算本周起始日期，并以 Y-m-d 形式返回。
function getWeekTime(id) {var Dy = Day - GDay;if (GDay == 0) {Dy -= 7;}if (id == "txtOrd_CreateTimeEnd") {Dy += 7;}var beginTime = "";if (Dy < 10) {beginTime = Year + "-" + Month + "-0" + Dy; //格式 Y-m-d
 } else {beginTime = Year + "-" + Month + "-" + Dy; //格式 Y-m-d
 }return beginTime;}//计算本月开始时间，并以Y-m-d 形式返回
function getMonthTime(id) { var Dy = 1;if (id == "txtOrd_CreateTimeEnd") {Dy = solarDays(Year, Month);}var beginTime = "";if (Dy < 10) {beginTime = Year + "-" + Month + "-0" + Dy; //格式 Y-m-d
 } else {beginTime = Year + "-" + Month + "-" + Dy; //格式 Y-m-d
 }return beginTime;}//计算今年开始时间，并以Y-m-d 形式返回
function getYearTime(id) {var beginTimes = "";if (id == "txtOrd_CreateTimeStart") {beginTimes = Year + "-01-01"; //格式 Y-m-d
 } else if (id == "txtOrd_CreateTimeEnd") {beginTimes = Year + "-12-31"; //格式 Y-m-d
 }return beginTimes;}//当月的天数
function solarDays(y, m) {var solarMonth = new Array(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);if (m == 2)return (((y % 4 == 0) && (y % 100 != 0) || (y % 400 == 0)) ? 29 : 28);elsereturn (solarMonth[m - 1]);}</script>