如果否则，则交换jQuery图像

Question

我正在尝试用javascript/jquery编写一个基本的图像交换。

由于某些原因，我的if/else语句没有正确运行。我是不是用错了？

谢谢

Javascript：

    <script type="text/javascript">
        var images = new Array();
        var comic = document.getElementById("comicssubsite").src;
        var artwork = document.getElementById("artworksubsite").src;
        var about = document.getElementById("aboutsubsite").src;

        images[0] = "./images/SiteDesign/Comics_subsites_hover.png";
        images[1] = "./images/SiteDesign/Comics_subsites.png";

        images[2] = "./images/SiteDesign/Artwork_subsites_hover.png";
        images[3] = "./images/SiteDesign/Artwork_subsites.png";

        images[4] = "./images/SiteDesign/About_subsites_hover.png";
        images[5] = "./images/SiteDesign/About_subsites.png";

        function onHover() {
            if (comic) {
            $("#comicssubsite").attr('src', images[0]);
            }
            else if (artwork) {
            $("#artworksubsite").attr('src', images[2]);
            }
            else if (about) {
            $("#aboutsubsite").attr('src', images[4]);
            }
        }
        function offHover() {
            if (comic) {
            $("#comicssubsite").attr('src', images[1]);
            }
            else if (artwork) {
            $("#artworksubsite").attr('src', images[3]);
            }
            else if (about)
            $("#aboutsubsite").attr('src', images[5]);
            }
        }

    </script>

HTML (代码段)

            <div class="span2">
                <div id="pages">
                    <span class="pageitems" ><a href="./?action=homepage&page=1&site=comics"><img id="comicssubsite" src="./images/SiteDesign/Comics_subsites.png" alt="comics bg" onmouseover="onHover();" onmouseout="offHover();"/></a></span>
                </div>
            </div>
            <div class="span2">
                <div id="pages">
                    <span class="pageitems"><a href="./?action=homepage&page=1&site=artwork"><img id="artworksubsite" src="./images/SiteDesign/Artwork_subsites.png" alt="artwork bg" onmouseover="onHover();" onmouseout="offHover();"/></a></span>    
                </div>
            </div>
            <div class="span2">
                <div id="pages">
                    <span class="pageitems"><a href="./?action=homepage&page=1"><img id="aboutsubsite" src="./images/SiteDesign/About_subsites.png" alt="about bg" onmouseover="onHover();" onmouseout="offHover();"/></a></span>
                </div>
            </div>

Answer 1

if语句检查各个元素的src属性是否不为空。这并不是你真正想要的--它们总是会被执行。此外，如果你已经决定使用jQuery，那么你应该在任何地方使用它，特别是在DOM方面，比如事件处理。

您使用数组作为数据结构是一个很好的开始，但是非常无用，因为您仍然手动地而不是通过编程来寻址这些项。使用对象文字作为键值映射，通过图像id获取urls：

jQuery(document).ready(function($) {
    var images = {
        "comicssubsite": [
            "./images/SiteDesign/Comics_subsites_hover.png",
            "./images/SiteDesign/Comics_subsites.png"
        ],
        "artworksubsite": [
            "./images/SiteDesign/Artwork_subsites_hover.png",
            "./images/SiteDesign/Artwork_subsites.png"
        ],
        "aboutsubsite": [
            "./images/SiteDesign/About_subsites_hover.png",
            "./images/SiteDesign/About_subsites.png"
        ]
    };
    function mouseover(e) {
        if (this.id in images) // check for key in map
            this.src = images[this.id][0];
    }
    function mouseout(e) {
        if (this.id in images)
            this.src = images[this.id][1];
    }
    $("#comicssubsite, #artworksubsite, #aboutsubsite").hover(mouseover, mouseout);
    // You might want to use a loop instead, then you don't need to write the ids twice:
    // for (var id in images)
    //     $('#'+id).hover(mouseover, mouseout);
});

Answer 2

您的第一个if语句总是返回true，因为每个图像标记都有一个源。

如果你有这个：

var comic = document.getElementById("comicssubsite").src;

然后是这个：

if (comic) {
//code
}

if语句所做的就是检查comic是否存在，它确实是这样做的。