face implemented by objects that can receive events and may have listeners for them." href="../../js/html/EventTarget.html">EventTarget</a></small></h4>    <span class="label label-meta label-meta-native" title="Rewrites the path of a type or class field during generation.">@:native(&quot;FetchObserver&quot;)</span></div><div class="body"><div class="doc doc-main"><p></p></div><h3 class="section">Variables</h3><div class="fields"><div class="field "><a name="onrequestprogress"></a><h3 class="anchor"><code><