title: javascript array index problem!
body: <p>var a = new array();
      a[1] = 'A';
      b[10] = 'B';
      console.log(a);
      /<em>[undefined, "A", undefined, undefined, undefined, undefined, undefined, undefined,
        undefined, undefined, "B"]</em>/
  I want to remove undefined element
  but what is the process??</p>