How to check jquery connection?

Question

JavaScript

Hello. I want to make a function with a call that checks if jquery is connected. If not connected, then connect, otherwise display alert. What am I doing wrong? How can I prevent jquery from being connected a second time when the function is called again?

function includejQuery() {
if (typeof jQuery === "undefined") 
{
    var script = document.createElement('script');
    script.type = "text/javascript";
    script.src = "catalog/view/javascript/libs.min.js";
    document.getElementsByTagName('head')[0].appendChild(script);

}else if (typeof jQuery != "undefined") {
alert('Jquery уже загружен');
}
}

<script>
includejQuery(function(){
$('.block').remove();
});
</script>
<div class="block">Привет!</div>

Answer 1

It's simple:

<script>window.jQuery || document.write('<script src="js/vendor/jquery-1.11.2.min.js"><\/script>')</script>