New to javascript: whats wrong with my mobile detection code?

Here is EVERYTHING from my .js file :

function isMobile() {
    Android: function() {
        return navigator.userAgent.match(/Android/i);
    },
    BlackBerry: function() {
        return navigator.userAgent.match(/BlackBerry/i);
    },
    iOS: function() {
        return navigator.userAgent.match(/iPhone|iPad|iPod/i);
    },
    Opera: function() {
        return navigator.userAgent.match(/Opera Mini/i);
    },
    Windows: function() {
        return navigator.userAgent.match(/IEMobile/i);
    },
    any: function() {
        return (isMobile.Android() || isMobile.BlackBerry() || isMobile.iOS() || isMobile.Opera() || isMobile.Windows());
    }
};

Additionally, in my html, I have the following if else statements and included ONLY the following in my header:

<script type="text/javascript" src="function.js" ></script>

The if else in my html is as follows:

<script>
            if( isMobile.any() ){
//load small video
}else{
//load full video
}

Now, I am a beginner. Can anyone tell me what might be wrong here? This is literally all the javascript related-ANYTHING in my code. Therefore if you know javascript, it might be obvious to you that something is missing, but don't assume that I have it and simply didn't add it to the post, because I don't. Like I said, this is literally everything. Any help?