Question

I have the following jquery code :

function InitVoteContainer(voteContainer) {

    var _userVote = voteContainer.children(".storeUserVote").val();
    var _userObjectId = voteContainer.children(".storeObjectId").val();
    var _userVoteKey = voteContainer.children(".storeVoteKey").val();
    var _UserAuth = voteContainer.children(".storeUserAuth").val();

    var _voteButtonUp = voteContainer.children("div[pid='btUp']");
    var _voteButtonDown = voteContainer.children("div[pid='btDown']");

    var upBtValue = 0;
    var downBtValue = 0;


        _voteButtonUp.attr("class", "upVote_inactive");
        _voteButtonDown.attr("class", "downVote_inactive");

        _voteButtonUp.prop("onclick", null);
        _voteButtonDown.prop("onclick", null);

}

The code will switch class on the upVote and downVote buttons. The code runs fine but the classes is never set? the question is why??

Edit 1:

Updates with some more code :

This jquery code runnes at dodument ready

function InitVoteControls() {

$("#mainPostList").find(".voteCon").each(function () {
    InitVoteContainer($(this));
});
}

And this is the HTML that the jquery is using :

<ul id="mainPostList" class="verticalList">
        @foreach (var postViewModel in Model.Posts)
        {
            <li>

<div class="postContainer">

<div class="voteCon">
        <input class="storeUserVote" type="hidden" value="@Model.UserVote" />
        <input class="storeObjectId" type="hidden" value="@Model.ObjectId" />
        <input class="storeVoteKey" type="hidden" value="@Model.VoteKey" />
        <input class="storeUserAuth" type="hidden" value="@Request.IsAuthenticated" />

        @if (!Request.IsAuthenticated)
        {
            <div pid="btUpVote" class="upVote"></div>
        }
        else
        {
            <div pid="btUpVote" class="upVote_inactive"></div>
        }

        <br style="clear:both;" />
        <div class="voteCountBox">
            @Html.Encode(Model.VoteBalance)
        </div>
        <br style="clear:both;" />

        @if (!Request.IsAuthenticated)
        {
            <div pid="btDownVote" class="downVote"></div>
        }
        else
        {
            <div pid="btDownVote" class="downVote_inactive"></div>
        }
</div>
</div>
</li>
        }
    </ul>

Answer 1

In your JavaScript you are selecting your button with

voteContainer.children("div[pid='btUp']");

which will return an emtpy jQuery object, since you have no div in your markup with the exact attribute pid='btUp'. You should use pid^='btUp' instead – or directly pid='btUpVote'.
See this example or the W3C specification.