Javascript ng-if 检查数组是否为空
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ng-if check if array is empty
提问by TheEks
The API I am working with returns this if there are no items in the array
如果数组中没有项目，我正在使用的 API 会返回此值
items: []
If there are items in the array it returns something like
如果数组中有项目，它会返回类似
items: [
{
name: 'Bla'
}
]
In my template I believe I need to use ng-if to either show/hide an element based on whether there is data in there or not.
在我的模板中，我相信我需要使用 ng-if 根据其中是否有数据来显示/隐藏元素。
<p ng-if="post.capabilities.items"><strong>Topics</strong>: <span ng-repeat="topic in post.capabilities.items">{{topic.name}}</p>
However I could be totally off base as this is my first time working in Angular, and there may be a much better way to do what I am trying to do.
但是，我可能会完全偏离基础，因为这是我第一次在 Angular 中工作，并且可能有更好的方法来做我想做的事情。
回答by Martijn Welker
post.capabilities.itemswill still be defined because it's an empty array, if you check post.capabilities.items.lengthit should work fine because 0is falsy.
post.capabilities.items仍然会被定义，因为它是一个空数组，如果你检查post.capabilities.items.length它应该可以正常工作，因为它0是假的。
回答by Dmitri Pavlutin
Verify the lengthproperty of the array to be greater than 0:
验证length数组的属性大于0：
<p ng-if="post.capabilities.items.length > 0">
<strong>Topics</strong>:
<span ng-repeat="topic in post.capabilities.items">
{{topic.name}}
</span>
</p>
Arrays (objects) in JavaScript are truthy values, so your initial verification <p ng-if="post.capabilities.items">evaluates always to true, even if the array is empty.
JavaScript 中的数组（对象）是真值，因此即使数组为空，您的初始验证也<p ng-if="post.capabilities.items">始终为true。
回答by Grant
To overcome the null/ undefinedissue, try using the ?operator to check existence:
要克服null/undefined问题，请尝试使用?运算符检查是否存在：
<p ng-if="post?.capabilities?.items?.length > 0">
Sidenote, if anyone got to this page looking for an Ionic Frameworkanswer, ensure you use
*ngIf:<p *ngIf="post?.capabilities?.items?.length > 0">
旁注，如果有人进入此页面寻找Ionic Framework答案，请确保您使用
*ngIf：<p *ngIf="post?.capabilities?.items?.length > 0">
