/* Example of Closure */

function foo(x) {
    var tmp = 3;
    return function(y) {
        alert(parseInt(x) + parseInt(y) + (++tmp));
    };
}

$(document).ready(function($) {
    $("#txtNum").val("10");
    var bar = foo(2);

    $("#testit").click(function() {
        bar($("#txtNum").val());
    });

}(jQuery));

<html>
    <body>
        <label id="lblNum" for="txtNum">Enter in a magic number:</label>
        <input type="textbox" id="txtNum" /><br/>
        <input type="button" id="testit" value="testit" />
        <label id="result"></label>
    </body>
</html>

jsFiddle