如何在pageload上加载第一个下拉选项

时间:2016-01-05 16:01:56

标签: javascript html

我希望有一个列出不同鸟类的下拉菜单,我希望每个选项都能显示该物种的唯一段落和图像。下面的代码几乎对我有用,但是在页面加载时我希望自动选择第一个选项。

  1. 我该怎么做?

  2. 这是解决这个问题的最好方法吗?

  3. 我是新手,我们非常感谢任何帮助。感谢

    https://jsfiddle.net/h0m0cpxk/

    
    
    <html>
    <body>
      
    <select id="opts" selected="selected" onchange="document.getElementById('ExtraInfo').firstChild.nodeValue = this.options[this.selectedIndex].getAttribute('extrainfo')">
      
      <option value="buzzard" extrainfo="The buzzard is by far the most common of all our birds of prey, and its expansion has been dramatic">Buzzard</option>
      <option value="redkite" extrainfo="The red kite is a medium-large bird of prey in the family Accipitridae, which also includes many other diurnal raptors such as eagles, buzzards, and harriers">Red kite</option>
      <option value="sparrowhawk" extrainfo="Habitat and food availability remain the main limiting and controlling factors of sparrowhawk numbers">Sparrow hawk</option>
      
    </select>
    
    <div id="ExtraInfo">extra</div>
    
    </body>
    </html>
    &#13;
    &#13;
    &#13;

2 个答案:

答案 0 :(得分:2)

一种简单的方法是默认情况下将第一个选项文本添加到ExtraInfo div。由于在加载页面时会自动选择选择列表中的第一个选项,因此它将满足您的需要。

<div id="ExtraInfo">The buzzard is by far the most common of all our birds of prey, and its expansion has been dramatic</div>

答案 1 :(得分:0)

将自动选择第一个选项。您可能不需要在此处触发更改事件。您可以将第一段写入HTML中的<p>;当您选择其他选项时,它将被覆盖。

另一种方法是在页面加载时通过Javascript触发onchange事件。没有jQuery,这有点棘手,请看这个问题:

https://stackoverflow.com/a/2856602/5742681