Add jQuery to a page.

jquerify.js

(function() {
    var b = document.getElementsByTagName('body')[0];
    otherlib = false;
    if (typeof jQuery != 'undefined') {
        console.log('This page already using jQuery v' + jQuery.fn.jquery);
    } else if (typeof $ == 'function') {
        otherlib = true;
    }
    function getScript(url, success) {
        var script = document.createElement('script');
        script.src = url;
        var head = document.getElementsByTagName('head')[0],
            done = false;
        script.onload = script.onreadystatechange = function() {
            if (!done && (!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete')) {
                done = true;
                success();
                script.onload = script.onreadystatechange = null;
                head.removeChild(script);
            }
        };
        head.appendChild(script);
    }
    getScript('//code.jquery.com/jquery-latest.min.js', function() {
        if (typeof jQuery == 'undefined') {
            console.log('Sorry, but jQuery wasn\'t able to load');
        } else {
            console.log('This page is now jQuerified with v' + jQuery.fn.jquery);
            if (otherlib) {
                console.log(' and noConflict(). Use $jq(), not $().');
                $jq = jQuery.noConflict();
            }
        }
        console.log('Call your function here.');
    });
})();