Serach String from Pagragraph using JavaScript?

<script type="text/javascript" language="JavaScript1.1">
<!--
// Declare variables
var pos = 0;
var num = -1;
var i = -1;
var graf = "This is a test This is a test  This is a test dsadasad This is a test adadasdsa This is a test fdsfdsfdsf This is a test  ";

// Search the string and counts the number of e's
while (pos != -1)
{
      pos = graf.indexOf("This is a test", i + 1);
      num += 1;
      i = pos;
}

// Write the response to the page
document.write(graf+"<br>")
document.write("There were " + num + " e's in that paragraph."); document.close();
//-->
</script>This is a test This is a test  This is a test dsadasad This is a test adadasdsa This is a test fdsfdsfdsf This is a test  <br>There were 6 e's in that paragraph.