[bes]

тут, кстати, есть тонкость

<script src="http://code.jquery.com/jquery-1.11.1.mind.js"></script>
<script>
if (typeof(jQuery) == "undefined") {
	document.write("<script src='jquery-1.11.1.js'></scr" + "ipt>"); 
}
console.log("typeof(jQuery) is " + typeof(jQuery));//undefined
</script>

<script>
console.log("typeof(jQuery) is " + typeof(jQuery));//function
</script>