What's wrong with my script that it doesn't allow auto-fullscreen?

Question

I want my page to be shown in full screen mode when loaded. I read this article How to make in Javascript full screen windows (stretching all over the screen)

And I am using the suggested solutions/codes for it. But it seems not working. I have the latest version of Chrome and I am sure it supports full screen mode. But it is still not working.

var elem = document.body; // Make the body go full screen.
requestFullScreen(elem);

function requestFullScreen(element) {
// Supports most browsers and their versions.
var requestMethod = element.requestFullScreen || element.webkitRequestFullScreen || element.mozRequestFullScreen || element.msRequestFullScreen;

if (requestMethod) { // Native full screen.
    requestMethod.call(element);
} else if (typeof window.ActiveXObject !== "undefined") { // Older IE.
    var wscript = new ActiveXObject("WScript.Shell");
    if (wscript !== null) {
            wscript.SendKeys("{F11}");
        }
    }
}

I also tried running this code under the load() event of jQuery.

$(document).load(function(){
    var elem = document.body;
    requestFullScreen(elem);
});

but both is not working. Could anyone please tell me what's the cause of this problem? Thank you.