I want to be able to populate the Rendered attribute of an apex:variable tag with the results of a function for different components i have, which are being displayed using <input> tags.

So let's say I am using Action Function like so:

<apex:variable value="x" var="y" rendered="{!myFunctionResult}"/>
<a>Input 1: </a>
<input name="input1"/>
<apex:actionFunction name="" immediate="true" action="{!function}">
<apex:param value="input1" name="fieldName"/>

</apex:actionFunction>

I am able to pass the input that I want to validate back to the controller function and I have a true/false returned, which I can then use to render the input.

How can I do this, so that when a page loads, this will occur automatically?

I want to be able to populate the Rendered attribute of an apex:variable tag with the results of a function for different components i have, which are being displayed using <input> tags.

So let's say I am using Action Function like so:

<apex:variable value="x" var="y" rendered="{!myFunctionResult}"/>
<a>Input 1: </a>
<input name="input1"/>
<apex:actionFunction name="" immediate="true" action="{!function}">
<apex:param value="input1" name="fieldName"/>

</apex:actionFunction>

I am able to pass the input that I want to validate back to the controller function and I have a true/false returned, which I can then use to render the input.

How can I do this, so that when a page loads, this will occur automatically?

[[ Updated ]] Still not working even when rerendering component...

<apex:component controller="FormExtensionController" > 
<apex:attribute type="String" description="test" name="fieldName" assignTo="{!fieldApiName}" />

<apex:outPutPanel id="mycomponent">
<apex:outPutPanel rendered="{!isRendered}">
<a>Input 1: </a>
</apex:outPutPanel>
</apex:outPutPanel>

<apex:form>
 <apex:actionFunction immediate="true" name="doCallout"  action="{!loadComponent}" rerender="mycomponent" />

</apex:form>
<script type="text/javascript">
(function() {
window.addEventListener("load", function() { doCallout(); });
})();
  </script>
  </apex:component>