jQuery async loader to page

jQueryLoader.js

function ensureJquery(readyCallback) {
    if (window.jQuery === undefined || parseFloat(window.jQuery.fn.jquery) < 1.9) {
        var js = document.createElement('script');
        js.src = "http://ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js";
        if (js.readyState)
            js.onreadystatechange = function () {
                if (this.readyState == 'complete' || this.readyState == 'loaded') {
                    jQueryLoadHandler();
                }
            };
        else
            js.onload = jQueryLoadHandler;
        (document.getElementsByTagName('head')[0] || document.documentElement).appendChild(js);
    } else {
        readyCallback(window.jQuery);
    }

    function jQueryLoadHandler() {
        readyCallback(window.jQuery.noConflict(true));
    }
}

@khaliullin, just noticed your comment. You call the method ensureJquery and provide callback, which will be called after:

• In case there is already loaded jQuery on page with version 1.9 or higher (you can change the version number)
• In case there is no jQuery on page at all, or it is lower than 1.9, then the method will load and inject it into page without conflicting with the version presented on the page

The callback that you specify will get an argument, which will be jQuery object in version 1.9 or higher without changing window global object jQuery.