javascript stop form submit if validation fails

1<form onsubmit = "event.preventDefault(); myValidation();">
2
3<script>
4  function myValidation()
5{
6   if(check if your conditions are not satisfying)
7   {
8      alert("Oops! Validation failed!");
9      returnToPreviousPage();
10      return false;
11   }
12   alert("Validations successful!");
13   return true;
14}
15  </script>