Frame Navigation

I have a back and next function. Back takes to the previous page and
Next takes to the next page. On some pages I want users to answer a
question before hitting the next button. If the users do not answer the
question the next displays an alert box. Now the following code does
that. But here is the PROBLEM

If you have answered the question once and you go back. You NEED NOT
answer the question again and clicking NEXT function will take you to
the next page

Each content page has a variable. The following goes on each top
content page
<script language="javascript">
var pageNext = "ab_04_01_0030" ;
var pageBack = "ab_04_01_0010" ;
eval("var " + pageBack + "answered = false"); // dynamic variable
set per page
</SCRIPT>

// The following functions are in another frame called navigation
function GoNext(page_name)
{
page_name = page_name + ".htm" ;
if (page_name != "#"){
var valu = top.Content.pageBack ; // Frame name is content
if (top.Content.eval(valu+ "answered") == true) {
top.Content.location.href = page_name;
}else{
alert("You need to answer the question");
CheckAnswer();
}
}
}

function CheckAnswer (){
var valu = top.Content.pageBack ;
top.Content.eval(valu+ "answered = true") ;
// temporarily sets that you have answer the question
}