How to stop form submit when onClick event returns false

I have the following code for my submit button

<input type="submit" name="action" value="Save Article"
onClick="this.v alue='Saving... '; performPrePostC hecks();">
[snip]
How come that irrespective of the function performPrePostC hecks
returning true, or false, that the form is still submitted?

Folks

I have the following code for my submit button

<input type="submit" name="action" value="Save Article"
onClick="this.v alue='Saving... '; performPrePostC hecks();">

I have tested performPrePostC hecks() - Its a long script, but I have proven its success by having an alert box echo the success with a simple true or
false message like so:

<script type="text/javascript">
function performPrePostC hecks()
{
if(checkRequire dFormFields('fo rm1','headline' ,'Headline')==f alse)
{ alert("false");
return false;
}

alert("true");
return true;
}
</script>
How come that irrespective of the function performPrePostC hecks returning
true, or false, that the form is still submitted?

Can someone point me in the right direction?

Thanks,
Randell D.

onClick="this.v alue='Saving... '; performPrePostC hecks();">

To clarify Eric's correct comments, you want:
onClick="this.v alue='Saving... '; return performPrePostC hecks();"

regards,
RR