title: JavaScript "new Array(n)" and "Array.prototype.map" weirdness
body: <p>I've observed this in Firefox-3.5.7/Firebug-1.5.3 and Firefox-3.6.16/Firebug-1.6.2</p>
  
  <p>When I fire up Firebug:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var x = new Array(3)
  console.log(x) 
  // [undefined, undefined, undefined]
  
  var y = [undefined, undefined, undefined]
  console.log(y) 
  // [undefined, undefined, undefined]
  
  console.log( x.constructor == y.constructor) // true
  
  console.log( 
    x.map(function() { return 0; })
  )
  // [undefined, undefined, undefined]
  
  console.log(
    y.map(function() { return 0; })
  )
  // [0, 0, 0]</code></pre>
  </div>
  </div>
  </p>
  
  <p>What's going on here?  Is this a bug, or am I misunderstanding how to use <code>new Array(3)</code>?</p>