form reload page code example

Example 1: why does my page reloads on form submission

//jquery method //
//preventDefault() prevents the submit button
//from performing its default task like page reload  
  $('#form').submit(function (e) {
      e.preventDefault();
  });

Example 2: why does my form reload the page? html js

document.getElementById("prospects_form").addEventListener('submit', function(event){event.preventDefault();});