JavaScript function to create HTML select option elements I made this function to get rid of writing numerical option values in a HTML-select manually.

From what I have seen so far it works as expected. But hints and suggestions are welcome anyway.



// Trying it out.
var selects = document.querySelectorAll('.drop-down');
selects = Array.prototype.slice.call(selects);

createOptions(selects[0], -9, 9, 8);

for (var i = 1; i &lt; selects.length; i++) {
  createOptions( selects[i], 
                 i * (-1 * Math.pow(10, i)),
                 i * Math.pow(10, i));
}

// The actual function ...

// The 1st Parameter is the HTML-element, the
// second is the bottom-limit, the third the
// upper limit. 
// The fourth, optional parameter allows to
// define the selected-option.

function createOptions( selectElement,
                        countOptionsStart,
                        countOptionsEnd,
                        preSelected ) {
    var bottom = countOptionsStart + '';
    var top = countOptionsEnd + '';
    var demand; // Count of needed chars.
  
    preSelected = preSelected || 0;
  
    var getLeadingZeros = function(demand, value) {
      var chars = value.toString() // Convert to string.
                       .split(''); // Make an array.
      // As long as the count of chars is less then
      // the demanded count iterate ...
      while (chars.length &lt; demand) {
        // If the first element in the array contains
        // an minus ('-') then use splice() for to
        // add a zero at index 1.
        if (chars[0] === '-') {
          chars.splice(1, 0, '0');
        } else {
          // ... otherwise add the zero at the 
          // beginning.
          chars.unshift('0');
        }
      }
      // Concat the array-elements to a string and
      // return this string.
      return chars.join('');
    }
    
    // The longer string is taken.
    demand = bottom.length &gt;= top.length ? bottom.length : top.length;
    
    // Constructing at adding the option-elements.
   for (var i = countOptionsStart; i &lt;= countOptionsEnd; i++) {
     var option = document.createElement('option');
     var optionInner;
      var innerHTML = i + '';
      
      if (innerHTML.length &lt; demand) 
        innerHTML = getLeadingZeros(demand, innerHTML);
      
      optionInner = document.createTextNode(innerHTML);
     option.setAttribute('value', i);
   
     if (i === preSelected) option.setAttribute('selected', 'selected');
   
     option.appendChild(optionInner);
     selectElement.appendChild(option);   
   }
}
&lt;select class="drop-down"&gt;&lt;/select&gt;
&lt;select class="drop-down"&gt;&lt;/select&gt;
&lt;select class="drop-down"&gt;&lt;/select&gt;
&lt;select class="drop-down"&gt;&lt;/select&gt;
Just a warning: in its current implementation your code works only if countOptionsStart is less than or equal to countOptionsEnd!
So depending on your actual needs you should check this case to exit without generating options, or adapt code to work also in this case.

In the other hand, I suggest you some improvements about process of filling value with zeroes. It dramatically reduces code size, and probably works faster:



// Trying it out.
var selects = document.querySelectorAll('.drop-down');
selects = Array.prototype.slice.call(selects);

createOptions(selects[0], -9, 9, 8);

for (var i = 1; i &lt; selects.length; i++) {
  createOptions( selects[i], 
                 i * (-1 * Math.pow(10, i)),
                 i * Math.pow(10, i));
}

function createOptions( selectElement,
                        countOptionsStart,
                        countOptionsEnd,
                        preSelected ) {
  preSelected = preSelected || 0;
  demand = Math.max(
    countOptionsStart.toString().length,
    countOptionsEnd.toString().length);
  for (var i = countOptionsStart; i &lt;= countOptionsEnd; i++) {
    var option = document.createElement('option'),
        strI = Math.abs(i) + '',
        sign = i &lt; 0 ? '-' : '',
        fill = i &lt; 0 ? demand -1 : demand;
    option.setAttribute('value', i);
    if (i === preSelected) option.setAttribute('selected', 'selected');
    option.innerHTML = sign + '0'.repeat(fill - strI.length) + strI;
    selectElement.appendChild(option);   
  }
}
&lt;select class="drop-down"&gt;&lt;/select&gt;
&lt;select class="drop-down"&gt;&lt;/select&gt;
&lt;select class="drop-down"&gt;&lt;/select&gt;
&lt;select class="drop-down"&gt;&lt;/select&gt;