How to get text from a textbox using javascript

i have developed a web application using mvc4.

in this case i need to get a text box value(actually the text entered in the text box) using javascript.

here is the code i am using

    @model PortalModels.WholeSaleModelUser    @using (Html.BeginForm("uploadFile", "WholeSaleTrade", FormMethod.Post, new { enctype = "multipart/form-data" }))    {        @Html.ValidationSummary(true)<fieldset><legend>WholeSaleModelUser</legend><table><tr><td><div class="editor-label">                        @Html.LabelFor(model => model.Name)</div></td><td><div class="editor-field">                        @Html.TextBoxFor(model => model.Name)                        @Html.ValidationMessageFor(model => model.Name)</div></td></tr></table><div id="partial"><table><tr><td><img id="blah" src="../../Images/no_image.jpg" alt="your image" height="200px" width="170px" /></td></tr></table><script type="text/javascript">        function loadUserImage() {            var userImg = document.getElementById("blah");            var imgNm = $("#Name").value;            userImg.src = "D:/FEISPortal/FortalApplication/Img/"+ imgNm +".png";            alert(imgNm);            alert(userImg.src);        }</script>

in that case alert gives the value as "undefined" and if do the following modification alert gives nothing.

var imgNm = document.getElementById("Name").value; 

for

var imgNm = $("#Name").value;

how to get the text entered in the text box?