一旦用户向下滚动页面150px，如何将图像显示为菜单项？

Question

I have a horizontal menu that is fixed to the top of the page and built by the following list:

<div id="menu">
  <ul id="nav">
    <li><a href="#">Home</a></li>
    <li><a href="#">blog</a></li>
    <li><a href="#">more info</a></li>
    <li><a href="#">contact</a></li>
  </ul>
</div>

Currently there is an empty space to the far left of the home menu link. How could I go about having an image of their logo show up in this location after the user scrolls down the page 150px?

I imagine this is a combo of javascript and CSS which is fine, I just need a roadmap of how to achieve the result. Thanks.

Answer 1

Place an element for the logo in the area you want it to be and provide it styling. Set it to display none at first.

Attach a scroll listener to the window. Check for if the page has scrolled 150px from the top. If it has change the display to block on the element with the logo. It if hasn't change the element to display none if it is visible.

Answer 2

You can do it with jQuery, if you'd like. The idea will be to go ahead and add the image, and then use JavaScript to add a class of hidden to the image (the image will be displayed whenever JavaScript is turned off, then), and then with jQuery, add or remove the class hidden depending on the scroll position.

<div id="menu">
  <img src="path/to/logo.png" id="logo">
  <ul id="nav">
    <li><a href="#">Home</a></li>
    <li><a href="#">blog</a></li>
    <li><a href="#">more info</a></li>
    <li><a href="#">contact</a></li>
  </ul>
</div>

/* CSS */

.hidden {
    display: none;
}

// jQuery
$(function() {
    var logo = $('#logo');

    logo.addClass('hidden');

    $(window).scroll(function() {
        if( +$(this).scrollTop > 149 ) {
            logo.removeClass('hidden');
        } else {
            logo.addClass('hidden');
        }
    });
});

Just as a note, if you would like the image to always be hidden if JavaScript is off, then hard-code class="hidden" into the HTML. When JavaScript is turned on, the code will still work the same. It's just a preference of how you want your page to behave with vs without JavaScript being on.

Answer 3

here is a little example how you can show/hide an element on page scroll with jQuery. hope this helps: http://jsfiddle.net/KWyS2/

<script type="text/javascript">
$(document).ready(function(){
    $(window).scroll(function(){
       var scrollTop     = $(window).scrollTop();
        $('.addDistance').html(scrollTop);
        if(scrollTop >= 150 ) {
            $('.show-hide-me').fadeIn();
        } else {
            $('.show-hide-me').fadeOut();
        }
    })
})
</script>

<div class="show-hide-me"></div>
<div class="content"></div>
<p class="addDistance"></p>

<style text="type/css">
.show-hide-me {
    display:none;
    width:100px;height:100px;
    background-color:orange;
    position:fixed;
    top:0px;
    left:0px;
}
.content {
    height:10000px;
    background-color:fuchsia;
    width:10px;
}
p {
    position:fixed;
    top:0px;right:0px;
    border:solid 1px red;
}
</style>