js日期和毫秒互转

<script>
function c1(){
    var d = document.getElementsByName("s")[0].value;
    var b = (new Date(d)).getTime();
    document.getElementsByName("s")[0].value = b;    
}
function c2(){
    var d = document.getElementsByName("d")[0].value;
    var b = new Date(d);
    b.setTime(d);
    document.getElementsByName("d")[0].value = b;    
}
</script>
 转毫秒<input name="s" value=""><input type="button" onclick="c1()" 

value="ssss" > 
转日期<input name="d" value=""><input type="button" 

onclick="c2()" value="dddd" >