一周内日期。

Question

前次网友给写了个，
但是不是很正确，会就算出4月33号来。。<input type="text" id="textyear" value="2009">年<input type="button" value="计算周数" onclick="getWeekNumber()"><span id="span1"></span>
<br/>
<input type="text" id="textweek" value="18">周<input type="button" value="计算日期" onclick="getDates()"><span id="span2"></span><script>
function getWeekNumber(){
    var theYear = document.getElementById("textyear").value;
    var firstDay = new Date(theYear + "/01/01");
    var counter = 0;
    while(firstDay.getFullYear() == theYear){
        firstDay.setDate(firstDay.getDate() + 7);
        counter++;
    }
    document.getElementById("span1").innerHTML = theYear + "年有" + counter + "周";
}function getDates(){
    var theYear = document.getElementById("textyear").value;
    var theWeek = document.getElementById("textweek").value;
    var theDay = new Date(theYear + "/01/01");
    theDay.setDate(theDay.getDate() + 7 * theWeek);
    while(theDay.getDay() != 1){
        theDay.setDate(theDay.getDate() - 1);
    }
    document.getElementById("span2").innerHTML = theYear + "年，第" + theWeek + "周：" 
        + theDay.getFullYear() + "-" + (theDay.getMonth() + 1) + "-" + theDay.getDate()
        + " ~ "
        + theDay.getFullYear() + "-" + (theDay.getMonth() + 1) + "-" + (theDay.getDate() + 6);
}
</script>
上面是网友给出的代码，周内的日期计算的不正确，那为大侠给该下，或发个正确的。

Answer 1

<input type="text" id="textyear" value="2009">年 <input type="button" value="计算周数" onclick="getWeekNumber()"> <span id="span1"> </span>
<br/>
<input type="text" id="textweek" value="18">周 <input type="button" value="计算日期" onclick="getDates()"> <span id="span2"> </span><script>
function getWeekNumber(){
    var theYear = document.getElementById("textyear").value;
    var firstDay = new Date(theYear + "/01/01");
    var counter = 0;
    while(firstDay.getFullYear() == theYear){
        firstDay.setDate(firstDay.getDate() + 7);
        counter++;
    }
    document.getElementById("span1").innerHTML = theYear + "年有" + counter + "周";
}function getDates(){
    var theYear = document.getElementById("textyear").value;
    var theWeek = document.getElementById("textweek").value;
    var theDay = new Date(theYear + "/01/01");
    theDay.setDate(theDay.getDate() + 7 * theWeek);
    while(theDay.getDay() != 1){
        theDay.setDate(theDay.getDate() - 1);
    }
    var endDay = new Date(theDay.getTime() + 7 * 24 * 60 * 60 * 1000);
    document.getElementById("span2").innerHTML = theYear + "年，第" + theWeek + "周："
        + theDay.getFullYear() + "-" + (theDay.getMonth() + 1) + "-" + theDay.getDate()
        + " ~ "
        + endDay.getFullYear() + "-" + (endDay.getMonth() + 1) + "-" + endDay.getDate();
}
</script>