Edit in JSFiddle

(function(){
    var getFlashPlayerVersion = function() {
        //[All] Flash Player is NOT installed.
        var version = 0;
        var tmp = [];
        try {
            //[IE] Flash Player is installed.
            var fo = new ActiveXObject('ShockwaveFlash.ShockwaveFlash');
            tmp = fo.GetVariable("$version").match(/([0-9]+)/);
            version = tmp[0];
        } catch (e) {
            if( navigator.mimeTypes ["application/x-shockwave-flash"] !== undefined ) {
                if( navigator.plugins && navigator.mimeTypes.length ) {
                    //[Other Browser] Flash Player is installed.
                    tmp = navigator.plugins["Shockwave Flash"].description.match(/([0-9]+)/);
                    version = tmp[0];
                }
            }
        }
        return version;
    };
 
    var version = getFlashPlayerVersion();
    var messageArea = document.getElementById("message");
    messageArea.innerText = (version) ? "Flash Player v"+version+"is installed!" :"Flash Player is not installed.";
 
})();

<h3>This is Javascript example getting the version of Flash Player. A function getFlashPlayerVersion returns the version, and when not installed, return 0 .</h3>
<span id="message"></span>

#message {
    color:red;
}