is the jquery.js functions denying me the ability to stop form submit?

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I am trying to either stop or permit the checkout form to submit itself based on the results of a confirm.

 

function showNotes(txt,btnValue) {
txt = txt || "Would you like to enter any notes / additional information for the staff?";
if (confirm(txt)) {
	jQuery("#notesField").slideDown();
	return false;
} else {
	jQuery("#submitFRMBTN").attr('value') = btnValue;
	return true;
}
}

<input type="submit" value="{$LANG.completeorder}"{if $cartitems==0} disabled{/if}{if $shownotesfield} onclick=" showNotes('{$LANG.orderenteradditionalnotes}','{$LANG.pleasewait}');"{/if} class="buttoncomplete" id="submitFRMBTN" />

I have tried numerous variations using return false, event.preventDefault(), event.stopPropagation() and tried using javascript instead of jQuery functions. However, no matter the code the form always submits.

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Anybody know?