Untitled

<body>
<apex:form >
    <apex:actionFunction name="doInit" action="{!initEndingPage}" rerender="allPanel"/>
    <apex:outputPanel id="allPanel">
        <apex:outputPanel rendered="{!NOT(endPageInit)}">
            <script type="text/javascript">
            window.onload=function() {
                doInit();
            };
            </script>
        </apex:outputPanel>
        <apex:outputPanel rendered="{!endPageInit}">
            <script>
                my javascript code
            </script>
        </apex:outputPanel>
    </apex:outputPanel>
</apex:form>