{{ DomRef() }}
概述
返回当前页面中获得焦点的元素,也就是说,如果此时用户按下了键盘上某个键,会在该元素上触发键盘事件.该属性是只读的.
很多情况下,该属性会返回一个{{ HTMLElement("input") }}或者{{ HTMLElement("textarea") }}元素,于此同时,如果用户在文本输入框中选中了一些文本,还可以使用该元素的selectionStart和selectionEnd属性获得准确的选中文本内容.
该属性的值还可能是一个{{ HTMLElement("select") }}元素(下拉菜单)或者type属性为button,checkbox或radio的{{ HTMLElement("input") }}元素.
注: 在Mac上,无法输入文字的元素无法获得焦点.
通常,用户可以通过Tab键来在页面中可以获得焦点的那些元素中切换,然后按下空格键激活这个元素(按下按钮,选择单选选项,打开下拉菜单选项等).
如果没有某个元素获得焦点,则该属性的值为当前页面中的{{ HTMLElement("body") }}元素.
注: 该属性被包含在了HTML5规范中.
语法
var curElement = document.activeElement;
示例
<!DOCTYPE HTML>
<html>
<head>
<script type="text/javascript" charset="utf-8">
function init() {
function onMouseUp(e) {
console.log(e);
var outputElement = document.getElementById('output-element');
var outputText = document.getElementById('output-text');
var selectedTextArea = document.activeElement;
var selection = selectedTextArea.value.substring(
selectedTextArea.selectionStart, selectedTextArea.selectionEnd);
outputElement.innerHTML = selectedTextArea.id;
outputText.innerHTML = selection;
}
document.getElementById("ta-example-one").addEventListener("mouseup", onMouseUp, false);
document.getElementById("ta-example-two").addEventListener("mouseup", onMouseUp, false);
}
</script>
</head>
<body onload="init()">
<div>
Select some text from one of the Textareas below:
</div>
<form id="frm-example" action="#" accept-charset="utf-8">
<textarea name="ta-example-one" id="ta-example-one" rows="8" cols="40">
This is Textarea Example One:
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec tincidunt, lorem a porttitor molestie, odio nibh iaculis libero, et accumsan nunc orci eu dui.
</textarea>
<textarea name="ta-example-two" id="ta-example-two" rows="8" cols="40">
This is Textarea Example Two:
Fusce ullamcorper, nisl ac porttitor adipiscing, urna orci egestas libero, ut accumsan orci lacus laoreet diam. Morbi sed euismod diam.
</textarea>
</form>
Active Element Id: <span id="output-element"></span><br/>
Selected Text: <span id="output-text"></span>
</body>
</html>
{{ JSFiddleLink("w9gFj") }}
规范
浏览器兼容性
{{ CompatibilityTable() }}
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
|---|---|---|---|---|---|
| Basic support | 2 | 3.0 | 4 | 9.6 | 4.0 |
| Feature | Android | Firefox Mobile (Gecko) | IE Phone | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|
| Basic support | {{ CompatUnknown() }} | {{ CompatUnknown() }} | {{ CompatUnknown() }} | {{ CompatUnknown() }} | {{ CompatUnknown() }} |