按左右箭头更改图像？

Question

所以我有这个简单的幻灯片：

<div class="container">
    <div id="slideshow">
        <img alt="slideshow" src="1.jpg" id="imgClickAndChange" onclick="changeImage()" />
    </div>
</div>

当我像这样单击时，我设法使图像发生变化：

<script language="javascript">
    var imgs = ["2.jpg", "3.jpg", "4.jpg", "5.jpg"];

    function changeImage() {
        document.getElementById("imgClickAndChange").src = imgs[0];
        imgs.push(imgs.shift())
    }
</script>

问题是我还希望在按右箭头（用于下一步）和左箭头（返回）时更改图像。 我该怎么做？ 我尝试添加一个“onkeypress”事件，但似乎没有任何效果。我做错了什么。我对javascript很陌生，所以如果你能帮助我，那就太好了。谢谢你:)

Answer 1

查看实际答案http://jsfiddle.net/7LhLsh7L/（提琴手注意：因为它在按箭头（左，右）键之前在编辑器本身中运行，您应该将焦点（只需单击结果区域）放在结果区域）

这是标记和脚本：

<div class="container">
    <div id="slideshow">
        <img alt="slideshow" src="http://thumb7.shutterstock.com/photos/thumb_large/253822/156271139.jpg" id="imgClickAndChange" onclick="changeImage()" />
    </div>
</div>
<script>
    var imgs = ["http://thumb7.shutterstock.com/photos/thumb_large/253822/156271139.jpg", "http://thumb9.shutterstock.com/photos/thumb_large/554278/132632972.jpg", "http://thumb7.shutterstock.com/photos/thumb_large/101304/133879079.jpg", "http://thumb101.shutterstock.com/photos/thumb_large/422038/422038,1327874090,3.jpg", "http://thumb1.shutterstock.com/photos/thumb_large/975647/149914934.jpg", "http://thumb9.shutterstock.com/photos/thumb_large/195826/148988282.jpg"];

    function changeImage(dir) {
        var img = document.getElementById("imgClickAndChange");
        img.src = imgs[imgs.indexOf(img.src) + (dir || 1)] || imgs[dir ? imgs.length - 1 : 0];
    }

    document.onkeydown = function(e) {
        e = e || window.event;
        if (e.keyCode == '37') {
            changeImage(-1) //left <- show Prev image
        } else if (e.keyCode == '39') {
            // right -> show next image
            changeImage()
        }
    }
</script>

上述方案的特点：

• 如果您单击图像，它将带您到下一张图像，并在到达最后一张图像时重复循环。
• 对于左箭头 (
• 右箭头 (->) 的行为类似于单击。

Answer 2

虽然您已经接受了答案，但我自己解决问题的方法是：

function imgCycle(e) {
    // obviously use your own images here:
    var imgs = ['nightlife', 'people', 'sports', 'cats'],
        // reference to the img element:
        imgElement = document.getElementById('imgClickAndChange'),
        // finding the string of the src after the last '/' character:
        curImg = imgElement.src.split('/').pop(),
        // finding that string from the array of images:
        curIndex = imgs.indexOf(curImg),
        // initialising the nextIndex variable:
        nextIndex;

    // if we have a keyCode (therefore we have a keydown or keyup event:
    if (e.keyCode) {
        // we do different things based on which key was pressed:
        switch (e.keyCode) {
            // keyCode 37 is the left arrow key:
            case 37:
                // if the current index is 0 (the first element in the array)
                // we next show the last image in the array, at position 'imgs.length - 1'
                // otherwise we show the image at the previous index:
                nextIndex = curIndex === 0 ? (imgs.length - 1) : curIndex - 1;
                break;
                // keyCode 39 is the right arrow key:
            case 39:
                // if curIndex + 1 is equal to the length of the images array,
                // we show the first element from the array, otherwise we use the next:
                nextIndex = curIndex + 1 === imgs.length ? 0 : curIndex + 1;
                break;
        }
        // if we don't have a keyCode, we check if the event-type (in lowercase)
        // is a mousedown:
    } else if (e.type.toLowerCase() === 'mousedown') {
        // I'm assuming you'd like to advance to the next image, rather
        // than regress to the previous (same check as above):
        nextIndex = curIndex + 1 === imgs.length ? 0 : curIndex + 1;
    }
    // setting the src of the image to the relevant URL + the string from the array
    // at the 'nextIndex':
    imgElement.src = 'http://lorempixel.com/200/200/' + imgs[nextIndex];
}

// binding a mousedown event-handler to the 'img' element:
document.getElementById('imgClickAndChange').addEventListener('mousedown', imgCycle);
// binding the keydown event-handler to the 'body' element:
document.body.addEventListener('keydown', imgCycle);

JS Fiddle demo.

参考资料：

• Array.prototype.indexOf()。
• Conditional ('ternary') operator (assessment ? ifTrue : ifFalse)。
• document.getElementById()。
• Event.keyCode。
• String.prototype.split()。
• String.prototype.toLowerCase()。

Answer 3

您可以检测 JavaScript 中的箭头键按下，然后将每个键附加到一个事件。 This SO answer 展示了它是如何完成的，但本质上是：

document.onkeydown = checkKey;

function checkKey(e) {

    e = e || window.event;

    if (e.keyCode == '37') {
        // left arrow
    }
    else if (e.keyCode == '39') {
        // right arrow
    }
}