javascript Jquery 检查元素是否存在以及条件是否存在
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Jquery check if element exist and if conditon
提问by Sasha
I have code like this:
我有这样的代码：
<?php if ($this->session->userdata('permission') == 4 || $this->session->userdata('permission') == 3) : ?>
<select name="caffe" id="caffe">
<?php foreach($caffe as $key) : ?>
<option value="<?php echo $key['id_caffe'] ?>"><?php echo $key['name'] ?></option>
<?php endforeach; ?>
</select>
<div id="gll_select">
<script>
var caffe = $("#caffe").val();
var cff_name = $("#caffe option:first").text();
$("#gll_select").load("<?php echo base_url() ?>form/galleries", {id : caffe}, function(){
$("#gll").on('change', function(){
var cff_name = $("#caffe option:selected").text();
get_gallery(cff_name);
console.log(cff_name);
});
});
</script>
</div>
<?php else : ?>
<input type="hidden" name="caffe_name" id="caffe_name" value="<?php echo $caffe_name ?>" />
<input type="hidden" name="caffe_id" id="caffe_id" value="<?php if(isset($caffe_id)) echo $caffe_id; ?>" />
<div id="gll_select">
<?php if (isset($gallery)) : ?>
<select name="gll" id="gll">
<?php foreach ($gallery as $key) : ?>
<option value="<?php echo $key['id_gallery'] . " " . $key['name'] ?>"><?php echo $key['name'] ?></option>
<?php endforeach; ?>
<?php endif; ?>
</select>
</div>
<?php endif ?>
and jquery code like this:
和 jquery 代码是这样的：
if ($("#caffe".length)){var cff_name = $("#caffe option:first").text(); }
else{var cff_name = $("#caffe_name").val();}
Problem is following - the first statement is always true (#caffewill not exist if PHP IF statement is FALSE). What seems to be the problem?
问题如下 - 第一个语句始终为真（如果#caffe将不存在PHP IF statement is FALSE）。似乎是什么问题？
回答by Pointy
Should be
应该
if ($("#caffe").length) { ... }
Your code:
您的代码：
if ($("#caffe".length)) { ... }
is getting the length of a string constant and passing that to jQuery. You always get a non-null result from a call to the jQuery main function ($), so the result of casting that to boolean as part of the ifstatement is always true.
正在获取字符串常量的长度并将其传递给 jQuery。您总是从对 jQuery 主函数 ($) 的调用中获得非空结果，因此将其转换为 boolean 作为if语句的一部分的结果始终为真。
When you instead test the .lengthproperty of the returned jQuery object made from a search for the selector, you're checking to see whether that number is non-zero.
当您测试通过.length搜索选择器生成的返回 jQuery 对象的属性时，您正在检查该数字是否为非零。
回答by safarov
Change $("#caffe".length)to $("#caffe").length
更改$("#caffe".length)为$("#caffe").length
回答by Surreal Dreams
I think I see the problem...
我想我看到了问题...
if ($("#caffe").length){var cff_name = $("#caffe option:first").text(); }
.lengthis not part of the selector, it's an attribute of the wrapped set.
.length不是选择器的一部分，它是包装集的一个属性。
