如何获得前一年的月份？

时间：2017-04-24 07:16:53

标签： javascript html

根据当月，我尝试获得上个月。但问题发生在＆＃34;年＆＃34;不是2017年。

enter image description here

那么我怎样才能获得上一年的月份？下面的代码将描述我想要的内容，如果有人知道如何获取它，请告诉我方法。谢谢:)）

＆＃13;
＆＃13; 
var month = new Array();
		month[0] = "January";
		month[1] = "February";
		month[2] = "March";
		month[3] = "April";
		month[4] = "May";
		month[5] = "June";
		month[6] = "July";
		month[7] = "August";
		month[8] = "September";
		month[9] = "October";
		month[10] = "November";
		month[11] = "December";

		var cur_month = new Date();
		var cur_month_now = month[cur_month.getMonth()];
		var pre_month_1 = month[cur_month.getMonth()-1];
		var pre_month_2 = month[cur_month.getMonth()-2];
		var pre_month_3 = month[cur_month.getMonth()-3];
		var pre_month_4 = month[cur_month.getMonth()-4];
		var pre_month_5 = month[cur_month.getMonth()-5];

		document.getElementById("cur_month").innerHTML = cur_month_now;
		document.getElementById("pre_month_1").innerHTML = pre_month_1;
		document.getElementById("pre_month_2").innerHTML = pre_month_2;
		document.getElementById("pre_month_3").innerHTML = pre_month_3;
		document.getElementById("pre_month_4").innerHTML = pre_month_4;
		document.getElementById("pre_month_5").innerHTML = pre_month_5;
＆＃13; 
<div class="dropdown">
	  <button class="btn btn-danger dropdown-toggle" type="button" data-toggle="dropdown">Select Month
	  <span class="caret"></span></button>
	  <ul class="dropdown-menu">
	    <li><a href="#" id="cur_month"></a></li>
	    <li><a href="#" id="pre_month_1"></a></li>
	    <li><a href="#" id="pre_month_2"></a></li>
	    <li><a href="#" id="pre_month_3"></a></li>
	    <li><a href="#" id="pre_month_4"></a></li>
	    <li><a href="#" id="pre_month_5"></a></li>
	  </ul>
	</div>
＆＃13;
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＆＃13;

4 个答案:

答案 0 :(得分：5)

由于month[-1]和month[-2]为undefined

，您的定义未定义

您需要在日期对象中实际进行日期操作，而不仅仅是从索引中获取日期。

使用此方法获取上个月的日期

function getPrevMonth(date) {
  date.setMonth(date.getMonth() - 1);
  return date;
}

根据需要多次调用此方法。

<强>演示 

function getPrevMonth(date) {
  date.setMonth(date.getMonth() - 1);
  return date;
}

var month = new Array();
month[0] = "January";
month[1] = "February";
month[2] = "March";
month[3] = "April";
month[4] = "May";
month[5] = "June";
month[6] = "July";
month[7] = "August";
month[8] = "September";
month[9] = "October";
month[10] = "November";
month[11] = "December";

var cur_month = new Date();
var cur_month_now = month[cur_month.getMonth()];
var pre_month_1 = month[getPrevMonth(cur_month).getMonth()];
var pre_month_2 = month[getPrevMonth(cur_month).getMonth()];
var pre_month_3 = month[getPrevMonth(cur_month).getMonth()];
var pre_month_4 = month[getPrevMonth(cur_month).getMonth()];
var pre_month_5 = month[getPrevMonth(cur_month).getMonth()];

document.getElementById("cur_month").innerHTML = cur_month_now;
document.getElementById("pre_month_1").innerHTML = pre_month_1;
document.getElementById("pre_month_2").innerHTML = pre_month_2;
document.getElementById("pre_month_3").innerHTML = pre_month_3;
document.getElementById("pre_month_4").innerHTML = pre_month_4;
document.getElementById("pre_month_5").innerHTML = pre_month_5;
<div class="dropdown">
  <button class="btn btn-danger dropdown-toggle" type="button" data-toggle="dropdown">Select Month
	  <span class="caret"></span></button>
  <ul class="dropdown-menu">
    <li>
      <a href="#" id="cur_month"></a>
    </li>
    <li>
      <a href="#" id="pre_month_1"></a>
    </li>
    <li>
      <a href="#" id="pre_month_2"></a>
    </li>
    <li>
      <a href="#" id="pre_month_3"></a>
    </li>
    <li>
      <a href="#" id="pre_month_4"></a>
    </li>
    <li>
      <a href="#" id="pre_month_5"></a>
    </li>
  </ul>
</div>

答案 1 :(得分：1)

让Date为你做环绕。我们可以对代码进行一些改进，请参阅注释：

// Array initializers are cleaner and less typing
var month = [
    "January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December"
];

var dt = new Date();
var cur_month_now = month[dt.getMonth()];
dt.setMonth(dt.getMonth() - 1); // Date handles wrapping to previous year
var pre_month_1 = month[dt.getMonth()];
dt.setMonth(dt.getMonth() - 1);
var pre_month_2 = month[dt.getMonth()];
dt.setMonth(dt.getMonth() - 1);
var pre_month_3 = month[dt.getMonth()];
dt.setMonth(dt.getMonth() - 1);
var pre_month_4 = month[dt.getMonth()];
dt.setMonth(dt.getMonth() - 1);
var pre_month_5 = month[dt.getMonth()];

document.getElementById("cur_month").innerHTML = cur_month_now;
document.getElementById("pre_month_1").innerHTML = pre_month_1;
document.getElementById("pre_month_2").innerHTML = pre_month_2;
document.getElementById("pre_month_3").innerHTML = pre_month_3;
document.getElementById("pre_month_4").innerHTML = pre_month_4;
document.getElementById("pre_month_5").innerHTML = pre_month_5;
<div class="dropdown">
  <button class="btn btn-danger dropdown-toggle" type="button" data-toggle="dropdown">Select Month
	  <span class="caret"></span></button>
  <ul class="dropdown-menu">
    <li>
      <a href="#" id="cur_month"></a>
    </li>
    <li>
      <a href="#" id="pre_month_1"></a>
    </li>
    <li>
      <a href="#" id="pre_month_2"></a>
    </li>
    <li>
      <a href="#" id="pre_month_3"></a>
    </li>
    <li>
      <a href="#" id="pre_month_4"></a>
    </li>
    <li>
      <a href="#" id="pre_month_5"></a>
    </li>
  </ul>
</div>

答案 2 :(得分：0)

你可以更简洁一些，并使用模运算符：

＆＃13;
＆＃13; 
var month = "January,February,March,April,May,June,July,August,September,October,November,December"
           .split(','),
    monthNum = 12 + new Date().getMonth();
Array.from(document.querySelectorAll('.dropdown-menu a'), function (elem, i) {
    elem.textContent = month[(monthNum-i)%12];
});
＆＃13; 
<div class="dropdown">
  <button class="btn btn-danger dropdown-toggle" type="button" data-toggle="dropdown">Select Month
  <span class="caret"></span></button>
  <ul class="dropdown-menu">
    <li><a href="#" id="cur_month"></a></li>
    <li><a href="#" id="pre_month_1"></a></li>
    <li><a href="#" id="pre_month_2"></a></li>
    <li><a href="#" id="pre_month_3"></a></li>
    <li><a href="#" id="pre_month_4"></a></li>
    <li><a href="#" id="pre_month_5"></a></li>
  </ul>
</div>
＆＃13;
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注意：最好使用textContent代替innerHTML，因为您要放置文字，而不是HTML。

答案 3 :(得分：0)

没什么新东西，但对于较小的js代码...

＆＃13;
＆＃13; 
function getPrevMonth(date, m) {
  date.setMonth(date.getMonth() - m);
  return date;
}

//no need for such array
locale = "en-us";//or e.g. navigator.languages[0]
var d = new Date();

for (var i=0; i<6; i++){
  //also worth trying: create element instead of writing to exiting ones only: https://www.w3schools.com/jsref/met_document_createelement.asp
  document.getElementById("pre_month_"+i).innerHTML =  getPrevMonth(d,1).toLocaleString(locale, { month: "long" });
}
＆＃13; 
<div class="dropdown">
  <button class="btn btn-danger dropdown-toggle" type="button" data-toggle="dropdown">Select Month
	  <span class="caret"></span></button>
  <ul class="dropdown-menu">
    <li>
      <a href="#" id="pre_month_0"></a>
    </li>
    <li>
      <a href="#" id="pre_month_1"></a>
    </li>
    <li>
      <a href="#" id="pre_month_2"></a>
    </li>
    <li>
      <a href="#" id="pre_month_3"></a>
    </li>
    <li>
      <a href="#" id="pre_month_4"></a>
    </li>
    <li>
      <a href="#" id="pre_month_5"></a>
    </li>
  </ul>
</div>
＆＃13;
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