jQuery 只追加一次 [英] jQuery append only once

问题描述

所以我有这个:

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);
    }
});

});

滚动时，我试图使导航固定，这可行，但我还想在 #nav div 中添加带有徽标图像的标签，这也有效，但它会附加在每个滚动条上，因此在滚动时我得到了 100 张徽标图像.

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.

我怎样才能让它只附加一次，并且当它滚动不超过 136px 时被删除?

How can I make it to append only once and when it's not scrolled more than 136px to be removed?

推荐答案

只需使用布尔值，

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;
                }
            }
        });
    });

小提琴

另一种方法是使用 $('#lilLogoID').is(':visible') 进行检查，但是这将搜索 img 并检查每个事件的可见性(这将慢)

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)

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