javascript - 用JavaScript添加前导零？

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How can I pad a value with leading zeros?
                            
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我需要在所有9个月的“第二天”文本框中的月份中添加前导零，并在10、11、12处将其保留。我不知道如何实现这一目标。

帮帮我！

$(document).ready(function(){

 var currentDate = new Date()
    var day = currentDate.getDate()
    if(day <= 9)
    day = '0'+day;
    var month = currentDate.getMonth() + 1
    if(month <= 9)
    month = '0'+month;
    var year = currentDate.getFullYear()
    document.getElementById("element_183").value =("" + month + "/" + day + "/" + year + "")

    function DateFromString(str){
        str = str.split(/\D+/);
        str = new Date(str[2],str[0]-1,(parseInt(str[1])+90));
        return MMDDYYYY(str);
    }

    function MMDDYYYY(str) {
        var ndateArr = str.toString().split(' ');
        var Months = 'Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec';
        return (parseInt(Months.indexOf(ndateArr[+1])/4)+1)+'/'+ndateArr[2]+'/'+ndateArr[3];
    }

    function Add90Days() {
        var date = $('#element_183').val();
        var ndate = DateFromString(date);
        return ndate;
    }

    $('#element_183').ready(function(){
        $('#element_184').val(Add90Days());
    });

});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
Enter date:<input type="text" id="element_183" readonly>
Next date:<input type="text" id="element_184" readonly>

最佳答案

尝试以下代码：

var currentDate = new Date();
//currentDate.setMonth(currentDate.getMonth() + 7);
var day = currentDate.getDate()
if(day <= 9)
day = '0'+day;
var month = currentDate.getMonth() + 1
if(month <= 9)
month = '0'+month;
var year = currentDate.getFullYear()
document.getElementById("element_183").value =("" + month + "/" + day + "/" + year + "")

function DateFromString(str){
  str = str.split(/\D+/);
  str = new Date(str[2],str[0]-1,(parseInt(str[1])+90));

  return str;
}

function MMDDYYYY(str) {
  var ndateArr = str.toString().split(' ');
  var Months = 'Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec';
  var str = new Date(str);

  var day = str.getDate();
  if(day <= 9)
  day = '0'+day;
  var month = str.getMonth() + 1
  if(month <= 9)
  month = '0'+month;
  var year = str.getFullYear()
  return ("" + month + "/" + day + "/" + year + "");
}

function Add90Days() {
  var date = $('#element_183').val();
  var ndate = MMDDYYYY(DateFromString(date));
  return ndate;
}

$('#element_183').ready(function(){
  $('#element_184').val(Add90Days());
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
Enter date:<input type="text" id="element_183" readonly>
Next date:<input type="text" id="element_184" readonly>