Hii..
Look at this,It might help.
Make your form onsubmit to return false and call repective function on button on click.
<form id="" onsubmit="return false;" width="">
<input type="submit" value="checkUser" onclick="yourFunction()">
</form>
Or if are using a hyperlink
<a href="javascript:void(0);" class="" name="chkUser" value="checkuser" onclick="yourFunction()">Log in</a>