document.activeElement

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Returns the currently focused element, that is, the element that will get keystroke events if the user types any. This attribute is read only.

Often this will return an <input> or <textarea> object, if it has the text selection at the time.  If so, you can get more detail by using the element's selectionStart and selectionEnd properties.  Other times the focused element might be a <select> element (menu) or an <input> element, of type button, checkbox or radio.

ๆณจ่จ˜: On Mac, elements that aren't text input elements tend not to get focus assigned to them.

Typically a user can press the tab key to move the focus around the page among focusable elements, and use the space bar to activate it (press a button, choose a radio).

Do not confuse focus with a selection over the document, consisting mostly of static text nodes.  See window.getSelection() for that.

When there is no selection, the active element is the page's <body>.

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This attribute is part of the in-development HTML 5 specification.

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var curElement = document.activeElement;

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<!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>

JSFiddle ใง็ขบ่ช

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Originally introduced as a proprietary DOM extension in Internet Explorer 4, this property also is supported in Opera and Safari (as of version 4).

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