title: How to get keys by initing an javascript array with "Array(arrayLength)"?
body: <p>I created an array like this:</p>
  
  <pre><code>let arrObj = Array(2)
  arrObj.push(1)
  console.log("-----init array with Array(2)-----")
  console.log(arrObj)
  console.log("---print index with foreach()-----")
  arrObj.forEach((_, index) =&gt; console.log(index))
  console.log("---print index with map()-----")
  arrObj.forEach((_, index) =&gt; console.log(index))
  console.log("---print index with every()-----")
  arrObj.every((_, v) =&gt; console.log(v))
  console.log("---print index with keys()-----")
  for (const v of arrObj.keys()) {
    console.log(v)
  }
  console.log("---print index with findIndex()-----")
  console.log(arrObj.findIndex((_, v) =&gt; v &gt;= 0))
  </code></pre>
  
  <p>and i got the result:</p>
  
  <pre><code>-----init array with Array(2)-----
  [ &lt;2 empty items&gt;, 1 ]
  ---print index with foreach()-----  
  2
  ---print index with map()-----      
  2
  ---print index with every()-----    
  2
  ---print index with keys()-----     
  0
  1
  2
  ---print index with findIndex()-----
  0
  </code></pre>
  
  <p>why i got the different results with <em>keys()</em> and others?</p>
  
  <p>i would appreciate it if someone can help me.</p>