JavaScript（或 jQuery）中是否有“重点”？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/2683742/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Is there a 'has focus' in JavaScript (or jQuery)?
提问by alex
Is there something I can do like this (perhap via a plugin)
有什么我可以做的吗（也许通过插件）
if ( ! $('form#contact input]').hasFocus()) {
$('form#contact input:first]').focus();
}
Basically, set focus to the first input, but only if the user has not already clicked into anything?
基本上，将焦点设置为第一个输入，但前提是用户尚未单击任何内容？
I know this will work too, but is there anything more elegant?
我知道这也可以，但还有什么更优雅的吗？
$(function() {
var focused = false;
$('form#contact input]').focus(function() {
focused = true;
});
setTimeout(function() {
if ( ! focused) {
$('form#contact input:first]').focus();
}
}, 500);
});
回答by cletus
There is no native solution but yes there is a more elegant way you can do it:
没有本地解决方案，但是有一种更优雅的方法可以做到：
jQuery.extend(jQuery.expr[':'], {
focus: "a == document.activeElement"
});
You're defining a new selector. See Plugins/Authoring. Then you can do:
您正在定义一个新的选择器。请参阅插件/创作。然后你可以这样做：
if ($("...").is(":focus")) {
...
}
or:
或者：
$("input:focus").doStuff();
回答by dclowd9901
$('input:focus')
$('input:focus')
It's CSS. You don't need to create a "custom selector." It already exists! http://www.w3schools.com/CSS/pr_pseudo_focus.asp
是 CSS。您不需要创建“自定义选择器”。它已经存在了！http://www.w3schools.com/CSS/pr_pseudo_focus.asp
Just attach whatever process you want to do to that selector, and it will weed it out if the element in question is not focused. I did this recently to keep a keyupfrom instantiating an email input error check when the e-mail input wasn't being used.
只需将您想要执行的任何过程附加到该选择器上，如果相关元素未获得焦点，它就会将其清除。我最近这样做是为了防止keyup在未使用电子邮件输入时实例化电子邮件输入错误检查。
If all you're trying to do is check if the user has focused on anything themselves, just do this:
如果您要做的只是检查用户自己是否专注于任何事情，请执行以下操作：
if($('input:focus').size() == 0){
/* Perform your function! */
}
回答by luiggitama
I had trouble with cletus approach, using jQuery 1.3.2 and Firefox 3.6.8, because the string "a == document.activeElement"was not a valid function.
我在使用 jQuery 1.3.2 和 Firefox 3.6.8 的 cletus 方法时遇到了麻烦，因为该字符串"a == document.activeElement"不是有效的函数。
I fixed it defining a function for the focuskey. In fact, all other keys defined in jQuery.expr[':']are defined as functions. Here's the code:
我修复了它，为focus键定义了一个函数。事实上，在jQuery.expr[':']中定义的所有其他键都定义为函数。这是代码：
jQuery.extend(jQuery.expr[':'], {
focus: function(e){ return e == document.activeElement; }
});
So, now it works as expected.
所以，现在它按预期工作。
However, I was experiencing some strange behaviour in Firefox 3.6.8 (maybe a bug in FF?). If I clicked on an input text while the page was rendering, and if I called is(":focus")on page load, I would get an error from the browser, reported by FireBug, and the script would break.
但是，我在 Firefox 3.6.8 中遇到了一些奇怪的行为（可能是 FF 中的错误？）。如果我在页面渲染时单击输入文本，并且如果我调用is(":focus")页面加载，我会从浏览器收到 FireBug 报告的错误，并且脚本会中断。
To solve this, I surrounded the code with a try...catchblock, returning falseon error. Use it if you want to prevent your users from experiencing the same error:
为了解决这个问题，我用一个try...catch块包围了代码，false在错误时返回。如果您想防止用户遇到相同的错误，请使用它：
jQuery.extend(jQuery.expr[':'], {
focus: function(e){
try{ return e == document.activeElement; }
catch(err){ return false; }
}
});
回答by SLaks
No, there isn't.
不，没有。
However, you can simulate it like this:
但是，您可以像这样模拟它：
$(':input')
.data('focused', false)
.focus(function() { $.data(this, 'focused', true); })
.blur(function() { $.data(this, 'focused', false); });
回答by user5185370
Frustratingly difficult to find a solution to this problem considering the solution is actually very simple:
考虑到解决方案实际上非常简单，很难找到解决此问题的方法：
if (document.activeElement == this) {
// has focus
}
if (document.activeElement != this) {
// does not have focus
}回答by kasp3r
There is a plugin http://plugins.jquery.com/project/focused
有一个插件http://plugins.jquery.com/project/focused
Also you can check Using jQuery to test if an input has focus
回答by ExEdzy
I know this is an old question, but may be my solution will help someone :)
我知道这是一个老问题，但我的解决方案可能会对某人有所帮助:)
since this didnt worked for me:
因为这对我不起作用：
if ($(this)!=$(document.activeElement)) { ... }
..were "this" is returned from blur function. So i did this:
..were "this" 是从 blur 函数中返回的。所以我这样做了：
if ($(document.activeElement).attr("class") != "input_textbox"){ ... }
回答by JohnFx
Here is a succinct way to do it.
这是一个简洁的方法。
$(document.activeElement)
or to plug it into your example..
或将其插入您的示例中..
if ($('form#contact input]')[0]!=$(document.activeElement)) { ... }
回答by Kafoso
$('*:focus')
(Necro ftw, but still valid and useful)
（Necro ftw，但仍然有效且有用）
