<h3 dir="auto">Version</h3>
<p dir="auto">2.6.10</p>
<h3 dir="auto">Reproduction link</h3>
<p dir="auto"><a href="https://codepen.io/anon/pen/pXjBQq" rel="nofollow">https://codepen.io/anon/pen/pXjBQq</a></p>
<h3 dir="auto">Steps to reproduce</h3>
<ol dir="auto">
<li>
<p dir="auto">Trigger the mousemove event in the result iframe of Codepen. The text "false" is changed to "true"</p>
</li>
<li>
<p dir="auto">Compare the two <code class="notranslate">&lt;progress&gt;</code> elements. One is indeterminate and the other is not</p>
</li>
</ol>
<h3 dir="auto">What is expected?</h3>
<p dir="auto">Both <code class="notranslate">&lt;progress&gt;</code> elements should be in an indeterminate state, i.e. not having a value attribute set.</p>
<h3 dir="auto">What is actually happening?</h3>
<p dir="auto">There are two <code class="notranslate">&lt;progress&gt;</code> elements here.</p>
<ol dir="auto">
<li>
<p dir="auto">The first has <code class="notranslate">:value="progress"</code> and progress === undefined (verified by the text "true")</p>
</li>
<li>
<p dir="auto">The second has <code class="notranslate">:value="undefined"</code></p>
</li>
</ol>
<p dir="auto">Even if both these effectively are identical (set <code class="notranslate">value</code> to undefined), they are rendered differently. The first is not indeterminate and the second is.</p>
<hr>
<p dir="auto">Note that this does not happen if the progress variable is set initially to undefined. It must be changed e.g. via the event callback.</p>
<p dir="auto">This worked as expected in 2.4.2 but not in 2.4.3 and later.</p>
<h3 dir="auto">Version</h3>
<p dir="auto">2.5.17</p>
<h3 dir="auto">Reproduction link</h3>
<p dir="auto"><a href="https://codesandbox.io/s/986x7y34v4?expanddevtools=1" rel="nofollow">https://codesandbox.io/s/986x7y34v4?expanddevtools=1</a></p>
<h3 dir="auto">Steps to reproduce</h3>
<p dir="auto">First of all, this is the first Issue I've created on this project. So I'll take this opportunity to thank all of the contributors and maintainers for the awesome and astonishing work they do for Vue. THANKS!</p>
<p dir="auto">Having a functional component and trying to use it inside a v-for produces a <code class="notranslate">Duplicate keys detected</code> error, even if using :key="". It's fixable by just converting the component to a non-functional one.</p>
<p dir="auto">According to my understanding of functional components and the way :key="" works, even functional components (without a state) should be :key-able, as that isn't related to the state of the component itself.</p>
<p dir="auto">According to Chris Fritz (<a href="https://twitter.com/ivansieder/status/1030374407515058177" rel="nofollow">https://twitter.com/ivansieder/status/1030374407515058177</a>) the issue is also present in earlier versions.</p>
<h3 dir="auto">What is expected?</h3>
<p dir="auto">The v-for renders the component without any error.</p>
<h3 dir="auto">What is actually happening?</h3>
<p dir="auto">The v-for renders the component with a <code class="notranslate">Duplicate keys detected</code> error.</p>