jquery：如果 ul 为空
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jquery: if ul is empty
提问by Justin
Okay I have a jQuery dialog box which has a form in it and I am at my wits end trying to figure this out... Lets see if I can verbalize what I am trying to do..
好的，我有一个 jQuery 对话框，里面有一个表单，我在我的智慧尽头试图解决这个问题......让我看看我是否可以用语言表达我正在尝试做的事情......
I have 3 text boxes. #apInterest, #apPaymentand #apPrincipalin that exact order.
我有 3 个文本框。 #apInterest，#apPayment并#apPrincipal按照这个确切的顺序。
basic english terms of what i am trying to do:
我正在尝试做的基本英语术语：
on keyup in #apInterestif .valis less than 0 or greater than 99.99 trigger an error.. else check ul#mylistif it has any li, if not .hide
在 keyup 中#apInterestif.val小于 0 或大于 99.99 触发错误.. else 检查ul#mylist它是否有任何li，如果没有.hide
on keyup in #apPaymentif .valis less than 0 trigger an error else check the list for lihide if not.
#apPayment如果.val小于 0 ，则在 keyup 上触发错误，否则检查列表是否li隐藏。
#apPrincipalis the same thing exactly as #apPayment
#apPrincipal完全一样 #apPayment
what I have right this moment
此刻我有什么权利
$('#apInterest').live("keyup", function(e) {
var parent = $('.inter').parents("ul:first");
if ($('#apInterest').val() < 0 || $('#apInterest').val() > 99.99) {
$('.inter').remove();
$('#mylist').append('<li class="inter">Interest Rate cannot be below 0 or above 99.99</li>');
$('#popuperrors').show();
$(this).addClass('error');
} else {
$(this).removeClass('error');
$('.inter').remove();
alert(parent.children().text);
if (parent.children().length == 0){
$('#popuperrors').hide();
}
}
});
Although I have also tried
虽然我也尝试过
if ($("#mylist :not(:contains(li))") ){
$('#popuperrors').hide();
}
I had a function similar to this for all 3 textboxes but none of what I have tried seems to work.. any ideas on how to complete this
我对所有 3 个文本框都有一个与此类似的功能，但我尝试过的所有功能似乎都不起作用..有关如何完成此操作的任何想法
回答by Wulf
if ($('#mylist li').length == 0) ...
回答by SimplGy
I like using the children()method because it reads nicely and it works even if you've already cached the selector for your ul. Here's what it looks like:
我喜欢使用这个children()方法，因为它读起来很好，即使你已经为你的 ul 缓存了选择器，它也能工作。这是它的样子：
$myList = $('#myList')
if ( $myList.children().length === 0 ) ...
回答by Joseph Silber
jQuery always returns an array of elements. If no matches were found, the array will be empty. An empty array in Javascript evaluates to true:
jQuery 总是返回一个元素数组。如果未找到匹配项，则数组将为空。Javascript 中的空数组计算结果为 true：
console.log( !![] ); // logs: true
You want to check the length of the returned set:
您要检查返回集的长度：
if ( ! $("#mylist li").length ){
$('#popuperrors').hide();
}
