title: javascript variable as subscript in an array
body: <p>I can't find this answer anywhere. I am learning javascript on myself so I guess this is basic.</p>
  
  <p>I want to assign a variable "count" as the subscript of an array.</p>
  
  <pre><code>var firstnumber = 200;
  var count = 1;
  var a;
  a[count] = firstnumber;
  </code></pre>
  
  <p>therefore to achieve the result as a[count] = 200</p>
  
  <p>is there anyway to do this?</p>