reg2.html

<script 
    src="//ajax.aspnetcdn.com/ajax/4.0/1/MicrosoftAjax.js" 
    type="text/javascript">
</script>
<script
    type="text/javascript"
    src="//ajax.aspnetcdn.com/ajax/jQuery/jquery-1.7.2.min.js">
</script>
<script type="text/javascript">
    var hostweburl;

    // Load the required SharePoint libraries.
    $(document).ready(function () {

        // Get the URI decoded URLs.
        hostweburl =
            decodeURIComponent(
                getQueryStringParameter("SPHostUrl")
        );

        // The js files are in a URL in the form:
        // web_url/_layouts/15/resource_file
        var scriptbase = hostweburl + "/_layouts/15/";

        // Load the js files and continue to
        // the execOperation function.
        $.getScript(scriptbase + "SP.Runtime.js",
            function () {
                $.getScript(scriptbase + "SP.js", execOperation);
            }
        );
    });

    function getParameterByName(name, url) {
        if (!url) url = window.location.href;
        name = name.replace(/[\[\]]/g, "\\$&");
        var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
            results = regex.exec(url);
        if (!results) return null;
        if (!results[2]) return '';
        return decodeURIComponent(results[2].replace(/\+/g, " "));
    }
 
 
 // SP.SOD.executeFunc('sp.js', 'SP.ClientContext', createListItem);//makes sure sp.js is loaded and then calls createListItem method
 
    function createListItem() {
        var clientContext = new SP.ClientContext.get_current();//if the page and the list are in same site.If list is in different site then use relative url instead of get_current
        var oList = clientContext.get_web().get_lists().getByTitle('Registration');
        var ID = getParameterByName('ID');
        var myParam = location.search.split('ID=')[1];

        var itemCreateInfo = new SP.ListItemCreationInformation();
        this.oListItem = oList.addItem(itemCreateInfo);
        oListItem.set_item('Title', 'My New Item!');
        oListItem.set_item('CourseID', ID);
        oListItem.update();

        clientContext.load(oListItem);
        clientContext.executeQueryAsync(
            Function.createDelegate(this, this.onQuerySucceeded), 
            Function.createDelegate(this, this.onQueryFailed)
        );
    }

    function onQuerySucceeded() {
        alert('Item created: ' + oListItem.get_id() + ID);
    }

    function onQueryFailed(sender, args) {
        alert('Request failed. ' + args.get_message() + 
            '\n' + args.get_stackTrace());
    }

    </script>

    <input type="button" value="Register Here" id="btnSub" onclick="createListItem();" />