Q:

jQuery append only once

So I have this: 
jQuery("document").ready(function($){

var nav = $('#nav');
var logo = '<img src="img/logo.png" />';

$(window).scroll(function () {
    if ($(this).scrollTop() > 136) {
        nav.addClass("nav-f");
        nav.append(logo);
    } else {
        nav.removeClass("nav-f");
        nav.remove(logo);
    }
});

});

When scrolling I'm trying to make the navigation to be fixed, which works, but I also want to add a  tag with the logo image in the #nav div, which also works but it appends on every scroll so when scrolling I get like 100 images of the logo. 
How can I make it to append only once and when it's not scrolled more than 136px to be removed?

A:

just use a boolean, 
jQuery("document").ready(function($){

    var nav = $('#nav');
    var logo = '<img id="lilLogo" src="img/logo.png" />';
    var visible = false;

    $(window).scroll(function () {
            if ($(this).scrollTop() > 136) {
                nav.addClass("nav-f");
                if(!visible) {
                    nav.append(logo);
                    visible = true;
                }
            } else {
                nav.removeClass("nav-f");
                if(visible)  {
                    $('#lilLogo').remove();
                    visible = false;
                }
            }
        });
    });

fiddle
The alternative is to check with $('#lilLogoID').is(':visible'), however this would then do a search for img and check visible on every event (which would be slow)

