本文翻译自：How to get the focused element with jQuery?
Using jQuery, how can I get the input element that has the caret's (cursor's) focus?使用jQuery，我如何获得具有插入符号（光标）焦点的输入元素？
Or in other words, how to determine if an input has the caret's focus?或者换句话说，如何确定输入是否具有插入符号的焦点？
#1楼
参考：/question/lJv3/如何使用jQuery获取焦点元素
#2楼
$( document.activeElement )
将检索它而无需按照jQuery文档中的建议搜索整个DOM树
#3楼
// Get the focused element:var $focused = $(':focus');// No jQuery:var focused = document.activeElement;// Does the element have focus:var hasFocus = $('foo').is(':focus');// No jQuery:elem === elem.ownerDocument.activeElement;
Which one should you use?你应该使用哪一个？quoting the jQuery docs :引用jQuery文档 ：
As with other pseudo-class selectors (those that begin with a ":"), it is recommended to precede :focus with a tag name or some other selector;与其他伪类选择器（以“：”开头的那些）一样，建议先于：使用标记名称或其他选择器进行聚焦;otherwise, the universal selector ("*") is implied.否则，隐含通用选择器（“*”）。In other words, the bare
$(':focus')is equivalent to$('*:focus').换句话说，裸$(':focus')相当于$('*:focus')。If you are looking for the currently focused element, $( document.activeElement ) will retrieve it without having to search the whole DOM tree.如果您正在寻找当前关注的元素，$（document.activeElement）将检索它而无需搜索整个DOM树。
The answer is:答案是：
document.activeElement
And if you want a jQuery object wrapping the element:如果你想要一个包装元素的jQuery对象：
$(document.activeElement)
#4楼
Try this:试试这个：
$(":focus").each(function() {alert("Focused Elem_id = "+ this.id );});
#5楼
I've tested two ways in Firefox, Chrome, IE9 and Safari.我在Firefox，Chrome，IE9和Safari中测试了两种方法。
(1).（1）。$(document.activeElement)works as expected in Firefox, Chrome and Safari.$(document.activeElement)在Firefox，Chrome和Safari中按预期工作。
(2).（2）。$(':focus')works as expected in Firefox and Safari.$(':focus')在Firefox和Safari中按预期工作。
I moved into the mouse to input 'name' and pressed Enter on keyboard, then I tried to get the focused element.我移动鼠标输入'name'并在键盘上按Enter键，然后我尝试获得聚焦元素。
(1).（1）。$(document.activeElement)returns the input:text:name as expected in Firefox, Chrome and Safari, but it returns input:submit:addPassword in IE9$(document.activeElement)在Firefox，Chrome和Safari中返回输入：text：name，但它返回输入：在IE9中提交：addPassword
(2).（2）。$(':focus')returns input:text:name as expected in Firefox and Safari, but nothing in IE$(':focus')返回输入：text：在Firefox和Safari中预期的名称，但在IE中没有
<form action=""><div id="block-1" class="border"><h4>block-1</h4><input type="text" value="enter name here" name="name"/> <input type="button" value="Add name" name="addName"/></div><div id="block-2" class="border"><h4>block-2</h4><input type="text" value="enter password here" name="password"/> <input type="submit" value="Add password" name="addPassword"/></div></form>
#6楼
How is it noone has mentioned..怎么没人提到..
document.activeElement.id
I am using IE8, and have not tested it on any other browser.我正在使用IE8，并没有在任何其他浏览器上测试它。In my case, I am using it to make sure a field is a minimum of 4 characters and focused before acting.在我的情况下，我正在使用它来确保一个字段至少4个字符并在表演之前集中注意力。Once you enter the 4th number, it triggers.输入第4个数字后，它会触发。The field has an id of 'year'.该字段的ID为“年份”。I am using..我在用..
if( $('#year').val().length >= 4 && document.activeElement.id == "year" ) {// action here}
