function loadFirst(filename, filetype) {
    if(filetype == "js") {
        var node = document.createElement('script');
        node.setAttribute("type", "text/javascript");
        node.setAttribute("async", true);
        node.setAttribute("src", filename);
    } else if(filetype == "css") {
        var node = document.createElement("link");
        node.setAttribute("rel", "stylesheet");
        node.setAttribute("type", "text/css");
        node.setAttribute("href", filename);
    }
    if(typeof node != "undefined") {
        var h = document.getElementsByTagName("head")[0];
        h.parentNode.insertBefore(node, h);
    }
}

/* Load all CSS first and JS files for your site here. */
window.addEventListener('load', function() {
    loadFirst("//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js", "js");
    loadFirst("//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css", "css");
    loadFirst("//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js", "js");
    loadFirst("//fonts.googleapis.com/css?family=Open+Sans:300&subset=latin,cyrillic-ext,latin-ext,cyrillic,greek-ext,greek,vietnamese", "css");
});

//loadFirst("//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js", "js");

<script async src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

$('.carousel').carousel({
    interval: 3000,
    pause: false
})

Uncaught ReferenceError: $ is not defined