Problem sa array i getElementById

Code:

function setInvisible() {
    var elems = new Array(4);
    elems[0] = "dataManagement";
    elems[1] = "programmingLanguages";
    elems[2] = "systemSoftware";
    elems[3] = "network";
     
    for (var i=0; i<=3;i++) {
         document.getElementById(elems[i]).style.display = "none";
            }

}

Code:
document.getElementById(elems[i]) has no properties
document.getElementById(elems[i]).style.display = "none";

Code:

for (var i=0; i<=3;i++) {
document.getElementById(elems[i]).style.display = "none";
}

Code:


function setInvisible()
{
   var elems =
   [
      "dataManagement",
      "programmingLanguages",
      "systemSoftware",
      "network"
   ];

   for (var i = 0; i < elems.length; i++)
   {
      var elem = document.getElementById(elems[i]);

      if (elem) elem.style.display = 'none';
   }

}

Code:

function setInvisible()
{
    $.each(
    [
          "dataManagement",
          "programmingLanguages",
          "systemSoftware",
          "network"
    ],

    function()
    {
          $(this).hide();
    });
}

Code:

<div id="bla bla" class="toggleVisibility"> ...

Code:

function setVisible()
{
    $(".toggleVisibility").show();
}

function setInvisible()
{
    $(".toggleVisibility").hide();
}

function toggleVisibility()
{
    $(".toggleVisibility").toggle();
}