How to assign a boolean value of an Primefaces selectBooleanCheckbox as parameter to a java script function?

I am using primefaces framework,

I have a javascript function and I want to assign checked value to fixedLoss javascript function. I call fixedLoss() function but I don't take checked value info with primefaces

<p:selectBooleanCheckbox id="fixedLossId" value="#{chargebackBean.selectedChargebackCategory.fixedLoss}">
<p:ajax event="change"  update="fixedLossDateTime"  oncomplete="fixedLoss()"></p:ajax>
                        </p:selectBooleanCheckbox>

/

<script>
    function fixedLoss() {
                if (fixedLossSelected ??) {
                 ...
                 }
                else {
                 ...
                }
 </script>