How to call add key values from web.config to javascript(.js) file ?

You can't call server-side code directly, you'll need your server code to render a javascript variable that has the data you need and then use that

On your aspx page (or view if you're using MVC)

<script>
    var mySetting = '<%=System.Configuration.ConfigurationManager.AppSettings["MySetting"]%>';
</script>
<script src="/scripts/test.js"></script>

test.js

$(document).ready(function () {
    if (typeof (mySetting) == "undefined"){
        // if you need to check if the variable has been defined you can do this
        return;
    }

    // even though mySetting is defined on your aspx page you can still use it in your js files
    // as long as they are included after the variable is defined
    alert(mySetting);
});