blocks|key|1115547|text|使用Attribute+Equals+Selector|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1115548|var+thevalue+=+'foo';
var+exists+=+0+!=+$('#select-box+option[value='%2Bthevalue%2B']').length;|code-block|syntax|javascript|1115549|如果选项的值是通过Javascript设置的，这将不起作用。在这种情况下，我们可以执行以下操作：|1115550|var+exists+=+false;
$('#select-box+option').each(function(){
++++if+(this.value+==+'bar')+{
++++++++exists+=+true;
++++++++return+false;
++++}
});|1115551|entityMap|0|LINK|mutability|MUTABLE|url|http://api.jquery.com/attribute-equals-selector/^0|2|P|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

Use the <a href="http://api.jquery.com/attribute-equals-selector/" rel="noreferrer">Attribute Equals Selector</a>

<pre><code>var thevalue = 'foo';
var exists = 0 != $('#select-box option[value='+thevalue+']').length;
</code></pre>

If the option's value was set via Javascript, that will not work. In this case we can do the following:

<pre><code>var exists = false;
$('#select-box option').each(function(){
 if (this.value == 'bar') {
 exists = true;
 return false;
 }
});
</code></pre>

blocks|key|1115602|text|以防您(或其他人)有兴趣在没有jQuery的情况下完成这项工作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1115603|var+exists+=+false;
for(var+i+=+0,+opts+=+document.getElementById('select-box').options;+i+<+opts.length;+%2B%2Bi)
+++if(+opts[i].value+===+'bar'+)
+++{
++++++exists+=+true;+
++++++break;
+++}|code-block|syntax|javascript|1115604|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|$]]

Just in case you (or someone else) could be interested in doing it without jQuery:

<pre><code>var exists = false;
for(var i = 0, opts = document.getElementById('select-box').options; i &lt; opts.length; ++i)
 if( opts[i].value === 'bar' )
 {
 exists = true; 
 break;
 }
</code></pre>

blocks|key|1115798|text|这里有另一个类似的选择。在我的例子中，我在构建选择列表时检查另一个框中的值。当我进行比较时，我总是遇到未定义的值，所以我这样设置我的检查：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1115799|if+(+$("#select-box+option[value='"+%2B+thevalue+%2B+"']").val()+===+undefined)+{+//do+stuff+}|code-block|syntax|javascript|1115800|我不知道这种方法是否更昂贵。|1115801|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Here is another similar option. In my case, I'm checking values in another box as I build a select list. I kept running into undefined values when I would compare, so I set my check this way:

<pre><code>if ( $("#select-box option[value='" + thevalue + "']").val() === undefined) { //do stuff }
</code></pre>

I've no idea if this approach is more expensive.

blocks|key|1115869|text|为什么不使用过滤器呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1115870|var+thevalue+=+'foo';++++
var+exists+=+$('#select-box+option').filter(function(){+return+$(this).val()+==+thevalue;+}).length;|code-block|syntax|javascript|1115871|松散比较之所以有效，是因为exists+>0为true，exists+==+0为false，所以您可以只使用|1115872|if(exists){
++++//+it+is+in+the+dropdown
}|1115873|或者将其组合：|1115874|if($('#select-box+option').filter(function(){+return+$(this).val()+==+thevalue;+}).length){
++++//+found
}|1115875|或者，当每个选择下拉菜单都有选择框类时，这将为您提供一个包含值的select(s)的jquery对象：|1115876|var+matched+=+$('.select-boxes+option').filter(function(){+return+$(this).val()+==+thevalue;+}).parent();|1115877|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

Why not use a filter?

<pre><code>var thevalue = 'foo'; 
var exists = $('#select-box option').filter(function(){ return $(this).val() == thevalue; }).length;
</code></pre>

Loose comparisons work because exists > 0 is true, exists == 0 is false, so you can just use

<pre><code>if(exists){
 // it is in the dropdown
}
</code></pre>

Or combine it:

<pre><code>if($('#select-box option').filter(function(){ return $(this).val() == thevalue; }).length){
 // found
}
</code></pre>

Or where each select dropdown has the select-boxes class this will give you a jquery object of the select(s) which contain the value:

<pre><code>var matched = $('.select-boxes option').filter(function(){ return $(this).val() == thevalue; }).parent();
</code></pre>

blocks|key|1330963|text|​|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1330964|if(!$('#select-box').find("option:contains('"+%2B+thevalue++%2B+"')").length){
//do+stuff
}|code-block|syntax|javascript|1330965|1330966|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|K|8|@]|9|@]|A|$E|F]]|$1|G|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|M|8|@]|9|@]|A|$]]]|I|$]]

<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>if(!$('#select-box').find("option:contains('" + thevalue + "')").length){
//do stuff
}</code></pre>
</div>
</div>

blocks|key|1331036|text|我知道这是一个老生常谈的问题，但这个问题效果更好。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1331037|if(!$('.dropdownName[data-dropdown="'+%2B+data["item"][i]["name"]+%2B+'"]+option[value="'%2Bdata['item'][i]['id']%2B'"]')[0]){
++//Doesn't+exist,+so+it+isn't+a+repeat+value+being+added.+Go+ahead+and+append.
++$('.dropdownName[data-dropdown="'+%2B+data["item"][i]["name"]+%2B+'"]').append(option);
}|code-block|syntax|javascript|1331038|正如您在本例中所看到的，我通过唯一标记data-dropdown+name和所选选项的值进行搜索。当然，你不需要这些来让它们工作，但我把它们包含进来，这样别人就可以看到你可以搜索多个值，等等。|1331039|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I know this is kind of an old question by this one works better.

<pre><code>if(!$('.dropdownName[data-dropdown="' + data["item"][i]["name"] + '"] option[value="'+data['item'][i]['id']+'"]')[0]){
 //Doesn't exist, so it isn't a repeat value being added. Go ahead and append.
 $('.dropdownName[data-dropdown="' + data["item"][i]["name"] + '"]').append(option);
}
</code></pre>

As you can see in this example, I am searching by unique tags data-dropdown name and the value of the selected option. Of course you don't need these for these to work but I included them so that others could see you can search multi values, etc.

blocks|key|1331049|text|if+($select.find('option[value='+%2B+val+%2B+']').length)+{...}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1331050|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 ($select.find('option[value=' + val + ']').length) {...}
</code></pre>

blocks|key|1116063|text|有了选择的html集合，你可以检查是否每个选择都有带有特定值的选项，并过滤那些不匹配条件的选项：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1116064|//get+select+collection:
let+selects+=+$('select')
//reduce+if+select+hasn't+at+least+one+option+with+value+1
.filter(function+()+{+return+[...this.children].some(el+=>+el.value+==+1)+});|code-block|syntax|javascript|1116065|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|$]]

Having html collection of selects you can check if every select has option with specific value and filter those which don't match condition:
<pre><code>//get select collection:
let selects = $('select')
//reduce if select hasn't at least one option with value 1
.filter(function () { return [...this.children].some(el =&gt; el.value == 1) });
</code></pre>

How can I, using JQuery, check if a value belongs to dropdown list or not?

Check if value is in select list with JQuery

jQuery

如何使用JQuery检查某个值是否属于下拉列表？

问使用JQuery检查值是否在选择列表中
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