I'm not sure if apex:form is supposed to show up as something on the HTML, but I don't see it and document.getElementById() is not finding it. This is what I have:

<apex:page id="parampage">
    <apex:form id="paramform">
      <apex:param name="param" id="param" value="123"/>

These are the results when I do a JS call:

  1. alert('{!$Component.parampage.paramform}') result: parampage:paramform (as expected)

  2. alert('{!$Component.parampage.paramform.param}') result: parampage:paramform:param (as expected)

  3. document.getElementById('{!$Component.parampage.paramform}') result: returns the expected object

  4. document.getElementById('{!$Component.parampage.paramform.param}') result: null


apex:param is a logical construct that represents a parameter to some "managed" element (e.g. an element that uses the apex namespace). Technically, your code shouldn't compile, as the documentation for this element states:

A parameter for the parent component.
The <apex:param> component can only be a child of the following components:

Regardless, it doesn't generate any sort of element that you can simply grab by HTML ID. Instead, it's used to define the parameters that will be placed into a given function call back on the server.

For example, within an apex:actionFunction, it defines values that can be passed by JavaScript, and those parameters will be passed to the controller.

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