a rendering instruction:</p>
<pre><code class="language-javascript">// Data model
var users = [
    {id: 1, name: &quot;John&quot;, key: &#39;a&#39;},
    {id: 2, name: &quot;Mary&quot;, key: &#39;b&#39;},
]

// Later on...
users[0].key = &#39;c&#39;

// AVOID
users.map(function(user){
    // The component for John will be destroyed and recreated
    return m(UserComponent, user)
})

// PREFER
users.map(function(user){
    // Key is specifically extracted: data model is given its own property
    return m(U