Question

我希望在用户向下滚动100px后更改元素的可见性。

我已经有了一些代码，

var fixed = false;
$(document).scroll(function() {
    if( $(this).scrollTop() >= 100 ) {
        if( !fixed ) {
            fixed = true;
            $('#logo-scroll').css({position:'fixed', display:'visible !important'});
        }
    } else {
        if( fixed ) {
            fixed = false;
            $('#logo-scroll').css({display:'none'});
        }
    }
});

JSFiddle

代码有两个问题。

它不会默认为不可见，我希望它开始不可见。
不再重复，当用户向上滚动时，它不会变回不可见。

更多详情，

我想制作类似this标题的内容，但正如您所看到的那样，您可以看到小徽标的 half ，以及较大徽标的一部分。它不会影响techcrunch，因为标题很小，但在我的网站上，确实如此。我已经制作了所有内容，我只需要在display:none中启动它，并在100px后显示。

Answer 1

使用：display:block;和display:none;

jsFiddle DEMO

将此添加到您的CSS：

#logo-scroll{ display:none; position:fixed; }

JQ：

var $logo = $('#logo-scroll');
$(document).scroll(function() {
    $logo.css({display: $(this).scrollTop()>100 ? "block":"none"});
});

顺便说一句：在TC页面上，只有CSS播放z-indexes。而已。所有元素在页面加载时都是可见的，它只是在大徽标下面显示为z-index下部元素的滚动。

普通 Javascript 就像 this ：

var win = window,
    docEl = document.documentElement,
    $logo = document.getElementById('logo-scroll');

win.onscroll = function(){
   var sTop = (this.pageYOffset || docEl.scrollTop)  - (docEl.clientTop || 0);
   $logo.style.display =  sTop > 100 ? "block":"none" ;
};

Answer 2

这个问题已经得到解答了。只是添加一个可能对其他人有用的更好的例子，它正是op想要的。

code and demo

已修改：从原始来源添加了实际代码。

<强> jQuery的：

// This function will be executed when the user scrolls the page.
$(window).scroll(function(e) {
    // Get the position of the location where the scroller starts.
    var scroller_anchor = $(".scroller_anchor").offset().top;

    // Check if the user has scrolled and the current position is after the scroller start location and if its not already fixed at the top 
    if ($(this).scrollTop() >= scroller_anchor && $('.scroller').css('position') != 'fixed') 
    {    // Change the CSS of the scroller to hilight it and fix it at the top of the screen.
        $('.scroller').css({
            'background': '#CCC',
            'border': '1px solid #000',
            'position': 'fixed',
            'top': '0px'
        });
        // Changing the height of the scroller anchor to that of scroller so that there is no change in the overall height of the page.
        $('.scroller_anchor').css('height', '50px');
    } 
    else if ($(this).scrollTop() < scroller_anchor && $('.scroller').css('position') != 'relative') 
    {    // If the user has scrolled back to the location above the scroller anchor place it back into the content.

        // Change the height of the scroller anchor to 0 and now we will be adding the scroller back to the content.
        $('.scroller_anchor').css('height', '0px');

        // Change the CSS and put it back to its original position.
        $('.scroller').css({
            'background': '#FFF',
            'border': '1px solid #CCC',
            'position': 'relative'
        });
    }
});

<强> HTML

<div class="container">
    <div class="test_content">
        Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus interdum metus nec neque convallis id interdum nibh aliquet. Nulla eget varius diam. Ut ut dolor dolor. Mauris vehicula sodales mi quis euismod. In sem metus, volutpat nec fringilla sed, fermentum ac turpis. Cras aliquam venenatis rutrum. Donec pharetra ante sit amet justo pellentesque nec consequat ante elementum. Ut imperdiet iaculis tortor, id pretium urna pharetra sit amet. Aenean pharetra nunc risus, ac scelerisque urna. Morbi dictum egestas augue, in euismod metus commodo ac. Duis nisl ante, consequat et tincidunt id, eleifend eu ante. Integer lectus velit, tempus eu feugiat et, adipiscing ut mauris.
    </div>

    <!-- This div is used to indicate the original position of the scrollable fixed div. -->
    <div class="scroller_anchor"></div>

    <!-- This div will be displayed as fixed bar at the top of the page, when user scrolls -->
    <div class="scroller">This is the scrollable bar</div>

    <div class="test_content">
        Quisque sollicitudin elit vitae diam consequat accumsan. Suspendisse potenti. Donec dapibus tortor at justo eleifend at pellentesque leo lobortis. Etiam ultrices leo et nulla iaculis eu facilisis augue fermentum. Pellentesque eu leo purus. Vestibulum bibendum, metus at bibendum blandit, lacus neque porttitor diam, id facilisis lectus mauris et leo. Donec adipiscing interdum lacus sed condimentum. In auctor sollicitudin orci, ac interdum risus aliquet ullamcorper. Curabitur mollis accumsan vulputate. Etiam adipiscing diam nec dui posuere ut tincidunt felis tristique. Vestibulum neque enim, placerat sed placerat commodo, consectetur ac mauris. Sed ultrices pretium nibh, a blandit libero imperdiet pulvinar. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae;
    </div>
    ...
</div>

<强> CSS：

.container{font-size:14px; margin:0 auto; width:960px}
.test_content{margin:10px 0;}
.scroller_anchor{height:0px; margin:0; padding:0;}
.scroller{background:#FFF; border:1px solid #CCC; margin:0 0 10px; z-index:100; height:50px; font-size:18px; font-weight:bold; text-align:center; width:960px;}

在页面滚动上更改元素样式

2 个答案:

jsFiddle DEMO