title: Get the indexes of javascript array elements that satisfy condition
body: <p>I have an array like this:</p>
  
  <pre><code>[{prop1:"abc",prop2:"qwe"},{prop1:"abc",prop2:"yutu"},{prop1:"xyz",prop2:"qwrq"}]
  </code></pre>
  
  <p>I'd like to get the index of all elements that satisfy a condition; in this case, when <code>prop1 == "abc"</code>.  So the desired output is something like <code>[0,1]</code>.</p>
  
  <p>Struggling to find a clean way of doing this?
  <code>indexes = a.findIndex(x =&gt; x.prop1==="abc")</code> will return <code>0</code> for the above array, because it stops at the first successful find.  </p>
  
  <p>I feel like I want something like this: <code>indexes = a.filtered(x.index() =&gt; x.prop1==="abc")</code></p>