how to add javascript file only one time
I am working on MVC appliction .I have a masterpage which is calling external javascript file and sometimes child page also calling the javascript file. i want if one time it is added by child page or masterpage it should not again add that Javascript file. please help me this i have done but is not working
 enter code here

<script type="text/javascript">

        $(document).ready(function () {
            var fileref1 = document.createElement('script')
            fileref1.type = "text/javascript";
            fileref1.src = "~/Scripts/testZoomPlugin.js";
            fileref1.Id = "testZoomJS";
            if (typeof fileref1 == "undefined") {
                $.getScript('~/Scripts/testZoomPlugin.js');
            }
            fileref1.src = "~/Scripts/jquery.ui.widget.min.js";
            fileref1.Id = "testWidget";

            if (typeof fileref1 == "undefined") {
                $.getScript('~/Scripts/jquery.ui.widget.min.js');
            }
            fileref1.src = "~/Scripts/jquery.ui.slider.min.js";
            fileref1.Id = "testSlider";
            if (typeof fileref1 == "undefined"){
                $.getScript('~/Scripts/jquery.ui.slider.min.js');
            }
            if(typeof fileref1=="undefined"){
                $.getScript('~/Scripts/jquery.ui.slider.min.js');
        });
how to add javascript file only one time
===

I am working on MVC appliction .I have a masterpage which is calling external javascript file and sometimes child page also calling the javascript file. i want if one time it is added by child page or masterpage it should not again add that Javascript file. please help me this i have done but is not working
 enter code here

<script type="text/javascript">

        $(document).ready(function () {
            var fileref1 = document.createElement('script')
            fileref1.type = "text/javascript";
            fileref1.src = "~/Scripts/testZoomPlugin.js";
            fileref1.Id = "testZoomJS";
            if (typeof fileref1 == "undefined") {
                $.getScript('~/Scripts/testZoomPlugin.js');
            }
            fileref1.src = "~/Scripts/jquery.ui.widget.min.js";
            fileref1.Id = "testWidget";

            if (typeof fileref1 == "undefined") {
                $.getScript('~/Scripts/jquery.ui.widget.min.js');
            }
            fileref1.src = "~/Scripts/jquery.ui.slider.min.js";
            fileref1.Id = "testSlider";
            if (typeof fileref1 == "undefined"){
                $.getScript('~/Scripts/jquery.ui.slider.min.js');
            }
            if(typeof fileref1=="undefined"){
                $.getScript('~/Scripts/jquery.ui.slider.min.js');
        });