return false is better because it prevents the default behavior of the event and also prevents the page from bubbling up. Note that this is only correct in jQuery event handlers.

form submit forbidden

//使用return false来禁用 form的默认submit事件。

<form  method="POST"   action="" id="search-form">
          <input type="text" name="keywords"  />
          <input type="submit" value="Search" id="sButton" onclick="loadXMLDoc('file.xml')" />
</form>

<script>
    window.onload = function() { 
        document.getElementById("search-form").onsubmit = function() { 
            loadXMLDoc('file.xml');
            return false;
        };
    };
</script>

$( "form" ).on( "submit", function( event ) {
event.preventDefault();
});

用jqeury也可以这么干