javascript - 我已经尝试在下拉列表中列出过去 20 年。但无法将其显示为 Year to Year 形式的范围

Question

我从今年过去了 20 年。但目前我希望它显示为年复一年。 例如:1992 - 1999 1999 - 2002 2003 - 2015

这是我的代码。

function populatedropdown(yearfield) {
  var today = new Date(),
      yearfield = document.getElementById(yearfield),
      beforeYears = 20
      thisyear = today.getFullYear();
  
  for (var year = thisyear-beforeYears, index = 0; 
           index <= beforeYears; 
           index++, year++) {
    yearfield.options[index] = new Option(year, year);
  }
  yearfield.value = thisyear;
    //select today's year
}

//populatedropdown(id_of_day_select, id_of_month_select, id_of_year_select)
window.onload = function() {
  populatedropdown("yeardropdown")
}

<td><select id="yeardropdown"/></td>

这是我希望拥有的理想输出

Answer 1

我不确定我是否正确理解了你的问题，但如果我理解了，它比你已经拥有的更容易:

function populatedropdown(yearfield) {
  var today = new Date(),
      yearfield = document.getElementById(yearfield),
      beforeYears = 20,
      thisYear = today.getFullYear(),
      firstYear = thisYear - beforeYears,
      yearRange = firstYear + ' - ' + thisYear;
  
  yearfield.options[0] = new Option(yearRange, yearRange);
  yearfield.value = yearRange;
}

//populatedropdown(id_of_day_select, id_of_month_select, id_of_year_select)
window.onload = function() {
  populatedropdown("yeardropdown")
}

<select id="yeardropdown"/>

---

更新

由于您已经更新了您的问题，这里是我提出的解决方案:

(function(d) {
  d.addEventListener('DOMContentLoaded', function() {
    var currentYear = new Date().getFullYear(),
        totalYears = 20,
        firstYear = currentYear - totalYears;    
    
    var fromYear = d.getElementById('fromYear'),
        toYear = d.getElementById('toYear');
    
    for (var i = firstYear; i <= currentYear; i++) {
      var opt = d.createElement('option');
      opt.value = i;
      opt.textContent = i;
      
      fromYear.appendChild(opt);
      toYear.appendChild(opt.cloneNode(true));
    }
    
    toYear.value = currentYear;
    
    /* if you don't want to disable the impossible selections, remove the code below */
    disableYears();
    
    fromYear.addEventListener('change', disableYears);
    toYear.addEventListener('change', disableYears);
    
    function disableYears(e) {
      [].forEach.call(fromYear.querySelectorAll('option'), function(opt, i) {
        opt.disabled = opt.value > toYear.value;
      });
      
      [].forEach.call(toYear.querySelectorAll('option'), function(opt, i) {
        opt.disabled = opt.value < fromYear.value;
      });
    }
    /* if you don't want to disable the impossible selections, remove the code above */
  });
})(document);

<select id='fromYear'></select>
<select id='toYear'></select>