blocks|key|216016|text|if+(typeof+$("#dataTable").data('timer')+!==+'undefined')
{
++++//+your+code+here
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|216017|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>if (typeof $("#dataTable").data('timer') !== 'undefined')
{
 // your code here
}
</code></pre>

blocks|key|216047|text|if+($("#dataTable").data('timer'))+{
++...
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|216048|注意:只有当数据属性不是空字符串或“False值”时才返回true，例如0或false。|unstyled|offset|length|style|CODE|216049|如果要检查数据属性是否存在，即使是空的，也要执行以下操作：|216050|if+(typeof+$("#dataTable").data('timer')+!==+'undefined')+{
++...
}|216051|entityMap^0|0|T|4|10|1|12|5|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|R|8|@$G|S|H|T|I|J]|$G|U|H|V|I|J]|$G|W|H|X|I|J]]|9|@]|A|$]]|$1|K|3|L|5|F|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$B|C]]|$1|O|3|-4|5|F|7|10|8|@]|9|@]|A|$]]]|P|$]]

<pre><code>if ($("#dataTable").data('timer')) {
 ...
}
</code></pre>

NOTE this only returns <code>true</code> if the data attribute is not empty string or a "falsey" value e.g. <code>0</code> or <code>false</code>.

If you want to check for the existence of the data attribute, even if empty, do this:

<pre><code>if (typeof $("#dataTable").data('timer') !== 'undefined') {
 ...
}
</code></pre>

blocks|key|2860960|text|您可以使用jQuery的hasData方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2860961|http://api.jquery.com/jQuery.hasData/|offset|length|2860962|2860963|+jQuery.hasData(+element+)的主要优点是，如果当前不存在数据对象，则它不会创建数据对象并将其与元素相关联。相反，jQuery.data(元素)总是向调用者返回一个数据对象，如果以前不存在数据对象，则创建一个。|blockquote|2860964|2860965|2860966|这将只检查您的元素上是否存在任何数据对象(或事件)，它不能确认它是否特别具有"timer“对象。|2860967|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|11|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@$D|W|E|X|1|Y]]|A|$]]|$1|F|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|G|3|H|5|I|7|10|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|11|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|12|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|13|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|C]]]]

You can use jQuery's hasData method. 

<a href="http://api.jquery.com/jQuery.hasData/">http://api.jquery.com/jQuery.hasData/</a>

<blockquote>
 The primary advantage of jQuery.hasData(element) is that it does not create and associate a data object with the element if none currently exists. In contrast, jQuery.data(element) always returns a data object to the caller, creating one if no data object previously existed.
</blockquote>

This will only check for the existence of any data objects (or events) on your element, it won't be able to confirm if it specifically has a "timer" object.

blocks|key|215781|text|var+data+=+$("#dataTable").data('timer');
var+diffs+=+[];

if(+data.length+>+0+)+{
for(var+i+=+0;+i+%2B+1+<+data.length;+i%2B%2B)+{
++++diffs[i]+=+data[i+%2B+1]+-+data[i];
}

alert(diffs.join(',+'));
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|215782|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>var data = $("#dataTable").data('timer');
var diffs = [];

if( data.length &gt; 0 ) {
for(var i = 0; i + 1 &lt; data.length; i++) {
 diffs[i] = data[i + 1] - data[i];
}

alert(diffs.join(', '));
}
</code></pre>

blocks|key|2861007|text|我发现这对于动态设置的数据元素效果更好：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2861008|if+($("#myelement").data('myfield'))+{
++...
}|code-block|syntax|javascript|2861009|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I've found this works better with dynamically set data elements:

<pre><code>if ($("#myelement").data('myfield')) {
 ...
}
</code></pre>

blocks|key|216068|text|您可以使用css属性选择进行检查|type|unstyled|depth|inlineStyleRanges|entityRanges|data|216069|if+($('#dataTable').is('[data-timer]'))+{
+++//+data-timer+attribute+exists
}|code-block|syntax|javascript|216070|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can check by css attribute selection with

<pre><code>if ($('#dataTable').is('[data-timer]')) {
 // data-timer attribute exists
}
</code></pre>

blocks|key|216085|text|为了提供与上面不同的答案，您可以使用Object.hasOwnProperty(...)检查它，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|216086|+if(+$("#dataTable").data().hasOwnProperty("timer")+){
+++++//+the+data-time+property+exists,+now+do+you+business!+.....
+}|code-block|syntax|javascript|216087|或者，如果您有多个要迭代的数据元素，则可以对.data()对象进行变量设置，然后像这样迭代它：|216088|+var+objData+=+$("#dataTable").data();
+for+(+data+in+objData+){
++++++if(+data+==+'timer'+){
++++++++++++//...do+the+do
++++++}
+}|216089|并不是说这个解决方案比这里的任何其他解决方案都要好，但至少它是另一种方法……|216090|entityMap^0|I|Q|0|0|M|7|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|10|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|R|$]]

In the interest of providing a different answer from the ones above; you could check it with <code>Object.hasOwnProperty(...)</code> like this:

<pre><code> if( $("#dataTable").data().hasOwnProperty("timer") ){
 // the data-time property exists, now do you business! .....
 }
</code></pre>

alternatively, if you have multiple data elements you want to iterate over you can variablize the <code>.data()</code> object and iterate over it like this:

<pre><code> var objData = $("#dataTable").data();
 for ( data in objData ){
 if( data == 'timer' ){
 //...do the do
 }
 }
</code></pre>

Not saying this solution is better than any of the other ones in here, but at least it's another approach...

blocks|key|218075|text|您可以创建一个非常简单的jQuery-plugin来查询以下内容的元素：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|218076|$.fn.hasData+=+function(key)+{
++return+(typeof+$(this).data(key)+!=+'undefined');
};|code-block|syntax|javascript|218077|然后，您可以简单地使用$("#dataTable").hasData('timer')|offset|length|style|CODE|218078|注意事项：|218079|218080|仅在值不存在(为false+)时才返回undefined；如果将其设置为false/null，则hasData()仍将返回与内置$.hasData()不同的值，后者仅检查是否设置了元素上的任何数据。|unordered-list-item|218081|218082|entityMap^0|0|0|B|W|0|0|0|8|5|J|9|10|5|16|4|1C|9|1S|B|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|X|8|@$I|Y|J|Z|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|10|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|11|8|@]|9|@]|A|$]]|$1|P|3|Q|5|R|7|12|8|@$I|13|J|14|K|L]|$I|15|J|16|K|L]|$I|17|J|18|K|L]|$I|19|J|1A|K|L]|$I|1B|J|1C|K|L]|$I|1D|J|1E|K|L]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|U|$]]

You can create an extremely simple jQuery-plugin to query an element for this:

<pre><code>$.fn.hasData = function(key) {
 return (typeof $(this).data(key) != 'undefined');
};
</code></pre>

Then you can simply use <code>$("#dataTable").hasData('timer')</code> 

Gotchas:

<ul>
<li>Will return <code>false</code> only if the value does not exist (is <code>undefined</code>); if it's set to <code>false</code>/<code>null</code> it <code>hasData()</code> will still return <code>true</code>.</li>
<li>It's different from the built-in <code>$.hasData()</code> which only checks if any data on the element is set.</li>
</ul>

blocks|key|218088|text|回答错误-请参阅end编辑|type|unstyled|depth|inlineStyleRanges|entityRanges|data|218089|让我在Alex的回答的基础上再做一些补充。|218090|为了防止在数据对象不存在时创建数据对象，我最好这样做：|218091|$.fn.hasData+=+function(key)+{
++++var+$this+=+$(this);
++++return+$.hasData($this)+&&+typeof+$this.data(key)+!==+'undefined';
};|code-block|syntax|javascript|218092|然后，在$this没有创建数据对象的情况下，$.hasData返回false，并且不会执行$this.data(key)。|offset|length|style|CODE|218093|编辑:仅当使用$.data(element,+key,+value)而不是element.data(key,+value)设置数据时，函数$.hasData(element)才有效。因此，我的答案是不正确的。|BOLD|218094|entityMap^0|0|0|0|0|4|5|M|9|X|5|19|F|0|0|1V|7|R|11|O|1X|I|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|W|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|X|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|Y|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|Z|8|@$M|10|N|11|O|P]|$M|12|N|13|O|P]|$M|14|N|15|O|P]|$M|16|N|17|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|18|8|@$M|19|N|1A|O|S]|$M|1B|N|1C|O|P]|$M|1D|N|1E|O|P]|$M|1F|N|1G|O|P]]|9|@]|A|$]]|$1|T|3|-4|5|6|7|1H|8|@]|9|@]|A|$]]]|U|$]]

Wrong answer - see EDIT at the end

Let me build on Alex's answer.

To prevent the creation of a data object if it doesn't exists, I would better do:

<pre><code>$.fn.hasData = function(key) {
 var $this = $(this);
 return $.hasData($this) &amp;&amp; typeof $this.data(key) !== 'undefined';
};
</code></pre>

Then, where <code>$this</code> has no data object created, <code>$.hasData</code> returns <code>false</code> and it will not execute <code>$this.data(key)</code>.

EDIT: function <code>$.hasData(element)</code> works only if the data was set using <code>$.data(element, key, value)</code>, not <code>element.data(key, value)</code>. Due to that, my answer is not correct.

blocks|key|2861107|text|或者结合一些香草JS|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2861108|if+($("#dataTable").get(0).hasAttribute("data-timer"))+{
++...
}|code-block|syntax|javascript|2861109|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Or combine with some vanilla JS

<pre><code>if ($("#dataTable").get(0).hasAttribute("data-timer")) {
 ...
}
</code></pre>

blocks|key|2861116|text|我需要一个简单的布尔值来处理。因为它是未定义的或不存在的，并且不是false，所以我使用!!来转换为布尔值：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2861117|var+hasTimer+=+!!$("#dataTable").data('timer');
if(+hasTimer+){+/*+.......+*/+}|code-block|syntax|javascript|2861118|另一种解决方案是使用filter：|2861119|if(+$("#dataTable").filter('[data-timer]').length!==0)+{+/*+.......+*/+}|2861120|entityMap^0|18|2|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|P|$]]

I needed a simple boolean to work with. Because it's undefined of not present, and not false, I use the <code>!!</code> to convert to boolean:

<pre><code>var hasTimer = !!$("#dataTable").data('timer');
if( hasTimer ){ /* ....... */ }
</code></pre>

An alternative solution would be using filter:

<pre><code>if( $("#dataTable").filter('[data-timer]').length!==0) { /* ....... */ }
</code></pre>

blocks|key|218114|text|如果您想区分空值和缺失值，可以使用jQuery进行如下检查。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|218115|<div+id="element"+data-foo="bar"+data-empty=""></div>

<script>
"foo"+in+$('#element').data();+//+true
"empty"+in+$('#element').data();+//+true
"other"+in+$('#element').data();+//+false
</script>|code-block|syntax|javascript|218116|所以从原始问题开始，你会这样做。|218117|if("timer"+in+$("#dataTable").data())+{
++//+code
}|218118|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If you want to distinguish between empty values and missing values you can use jQuery to check like this.

<pre><code>&lt;div id="element" data-foo="bar" data-empty=""&gt;&lt;/div&gt;

&lt;script&gt;
"foo" in $('#element').data(); // true
"empty" in $('#element').data(); // true
"other" in $('#element').data(); // false
&lt;/script&gt;
</code></pre>

So from the original question you'd do this.

<pre><code>if("timer" in $("#dataTable").data()) {
 // code
}
</code></pre>

blocks|key|2861268|text|在我看来，这是最简单的解决方案，就是选择所有具有特定数据属性的元素：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2861269|var+data+=+$("#dataTable[data-timer]");
var+diffs+=+[];

for(var+i+=+0;+i+%2B+1+<+data.length;+i%2B%2B)+{
++++diffs[i]+=+data[i+%2B+1]+-+data[i];
}

alert(diffs.join(',+'));|code-block|syntax|javascript|2861270|这是它的工作原理的截图。|2861271|​|2861272|📷|atomic|offset|length|2861273|2861274|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/19d0b64ebd41d8f2713203203b47dc28.png|imageAlt^0|0|0|0|0|0|1|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|11|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|12|8|@]|9|@]|A|$]]|$1|K|3|L|5|M|7|13|8|@]|9|@$N|14|O|15|1|16]]|A|$]]|$1|P|3|J|5|6|7|17|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X|Y|-4]]]]

This is the easiest solution in my opinion is to select all the element which has certain data attribute:

<pre><code>var data = $("#dataTable[data-timer]");
var diffs = [];

for(var i = 0; i + 1 &lt; data.length; i++) {
 diffs[i] = data[i + 1] - data[i];
}

alert(diffs.join(', '));
</code></pre>

<h3>Here is the screenshot of how it works.</h3>

<a href="https://i.stack.imgur.com/s5ezJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/s5ezJ.png" alt="console log of the jquery selector"></a>

blocks|key|216004|text|那下面呢：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|216005|if+($('#dataTable[data-timer]').length+>+0)+{
++++//+logic+here
}|code-block|syntax|javascript|216006|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

And what about:

<pre><code>if ($('#dataTable[data-timer]').length &gt; 0) {
 // logic here
}
</code></pre>

blocks|key|216239|text|这里的所有答案都使用jQuery库。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|216240|但是vanilla+javascript非常简单。|216241|如果只想在id为#dataTable的元素也具有data-timer属性时运行脚本，则步骤如下：|offset|length|style|CODE|216242|//+Locate+the+element
const+myElement+=+document.getElementById('dataTable');

//+Run+conditional+code
if+(myElement.dataset.hasOwnProperty('timer'))+{

++[...+CODE+HERE...]

}|code-block|syntax|javascript|216243|entityMap^0|0|0|5|2|8|A|O|A|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|S|8|@$F|T|G|U|H|I]|$F|V|G|W|H|I]|$F|X|G|Y|H|I]]|9|@]|A|$]]|$1|J|3|K|5|L|7|Z|8|@]|9|@]|A|$M|N]]|$1|O|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|P|$]]

All the answers here use the jQuery library.
But the vanilla javascript is very straightforward.
If you want to run a script only if the element with an <code>id</code> of <code>#dataTable</code> also has a <code>data-timer</code> attribute, then the steps are as follows:
<pre><code>// Locate the element
const myElement = document.getElementById('dataTable');

// Run conditional code
if (myElement.dataset.hasOwnProperty('timer')) {

 [... CODE HERE...]

}
</code></pre>

Is there some way that I can run the following:

<pre><code>var data = $("#dataTable").data('timer');
var diffs = [];

for(var i = 0; i + 1 &lt; data.length; i++) {
 diffs[i] = data[i + 1] - data[i];
}

alert(diffs.join(', '));
</code></pre>

Only if there is an attribute called data-timer on the element with an id of #dataTable?

Is there a way that I can check if a data attribute exists?

jQuery

有没有什么方法可以让我运行以下代码：var data = $("#dataTable").data('timer');var diffs = [];for(var i = 0; i + 1 < data.length; i++) { diffs[i] = data[i + 1] - data[i];}alert(...

问有没有办法可以检查数据属性是否存在？
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问有没有办法可以检查数据属性是否存在？
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