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gistfile1.js

(function() {
    var el = document.createElement('div'),
	    b = document.getElementsByTagName('body')[0],
	    otherlib = false,
	    msg = '';
    el.style.position = 'fixed';
    el.style.height = '32px';
    el.style.width = '220px';
    el.style.marginLeft = '-110px';
    el.style.top = '0';
    el.style.left = '50%';
    el.style.padding = '5px 10px';
    el.style.zIndex = 1001;
    el.style.fontSize = '12px';
    el.style.color = '#222';
    el.style.backgroundColor = '#f99';
    if (typeof jQuery != 'undefined') {
        msg = 'This page already using jQuery v' + jQuery.fn.jquery;
        return showMsg();
    } 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('http://code.jquery.com/jquery-latest.min.js', 
	    function() {
	    	msg = "it worked."
	        return showMsg();
    });
    function showMsg(){
    	el.innerHTML=msg;b.appendChild(el);
		if(otherlib){
			$jq=jQuery.noConflict();
		}
    }
})();