Create the following HTML and you could figure out how to generate random number by Javascript.

<script type="text/javascript">
  // Random float number between 0 and 1
  document.write(Math.random() + "<br />");

  // Random integer between 0 and 10
  document.write(Math.floor(Math.random()*11));
</script> 

Done =)

Reference: W3Schools – JavaScript random() Method