Unless you are actually using an iFrame there isn't a "parent" page/ "child" page. All the elements are within the same Document. Having one part update doesn't really matter as long as those updates use consistent language/definitions as the initial update. For instance, I have a div I will give an id of "dynamicDiv" and that div contains a table with checkboxes.
<div id='dynamicDiv'>
<table><tbody>
<tr><td><input type='checkbox' class='selectRow'></td></tr>
<tr><td><input type='checkbox' class='selectRow'></td></tr>
<tr><td><input type='checkbox' class='selectRow'></td></tr>
<tr><td><input type='checkbox' class='selectRow'></td></tr>
</tbody></table>
</div>
<div><a href='javascript:void(0)' id='checkall'>Check All</a></div>
Now when you click the check all button I'm assuming you want all of the checkboxes to become selected. Using just javascript we could do:
<script>
window.onload = function()
{
document.getElementById("checkall").onClick = function()
{
var dynamicDiv = document.getElementById("dynamicDiv");
var inputs = dynamicDiv.getElementsByTagName("input");
for(var i = 0; i < inputs.length; i++)
{
if(inputs[i].className == "selectRow")
{
inputs[i].checked = true;
}//else we ignore
}
}
}
</script>
You make the code above shorter by introducing a javascript framework such as JQuery, but unless you understand the long way debugging down the road will just trip you up.