以下代码可在实时站点上运行，但无法在jsfiddle站点上运行。

谁能告诉我为什么它在jsfiddle上不起作用？

在控制台上，它记录：ReferenceError: fillList is not defined和ReferenceError: mySelectList is not defined。

您将代码作为片段嵌入此处时，可以看到该代码的工作原理：

function BetterSelect(oSelList) {

  this.objSelectList = oSelList;

  this.objSelectList.onchange = this.selectionChanged;

}

BetterSelect.prototype.clear = function() {

  this.objSelectList.options.length = 0;

}

BetterSelect.prototype.fill = function(aValues) {

  this.clear();

  for (var i = 0; i < aValues.length; i++) {

    this.objSelectList.options[i] = new Option(aValues[i]);

  }

}

BetterSelect.prototype.find = function(strToFind, bSelect) {

  var indx = -1;

  this.objSelectList.options.selectedIndex = -1;

  for (var i = 0; i < this.getCount(); i++) {

    if (this.objSelectList.options[i].text == strToFind) {

      indx = i;

      if (bSelect)

        this.objSelectList.options.selectedIndex = i;

    }

  }

  return indx;

}

BetterSelect.prototype.getCount = function() {

  return this.objSelectList.options.length;

}

BetterSelect.prototype.selectionChanged = function() {

  alert("selection changed!");

}



var mySelectList = null;

window.onload = function() {

  mySelectList = new BetterSelect(document.getElementById('theList'));

}



function fillList() {

  mySelectList.fill(["one", "two", "three", "four", "five"]);

}



function findIt() {

  mySelectList.find(document.getElementById('txtToFind').value, true);

}


<form action="" method="post">

  <select multiple="multiple" name="Select1" id="theList" style="width: 152px; height: 226px">

  </select>

  <br />

  <input name="Button1" type="button" value="Fill The List" onclick="fillList()" />

  <input name="Button4" onclick="mySelectList.clear()" type="button" value="Clear The List" />

  <br />

  <input name="Button2" onclick="alert(mySelectList.getCount())" type="button" value="What's The Count?" />

  <br />

  <input name="Text1" type="text" id="txtToFind" />

  <input name="Button3" type="button" value="Search" onclick="findIt()" />

</form>