molendijk

The javascript location.search propery sets / returns the query portion of a URL, including the question mark (?). This means that if we put <a onclick="location.search='this is a test'">test</a> in a file named our_file.html, the URL (our_file.html) will be replaced with our_file.html?this is a test after a click on the link. Having arrived at our_file.html?this is a test, we can go back to our_file.html by using the browser's history (back) button. The content of our_file.html?this is a test will be identical to the content of our_file.html, unless we do something about it. And we should, because having two identical pages on a site is not a very useful thing.

We can use the search portion of a URL containing a question mark - where the search portion is the string to the right of '?' - to pass data from one page (our_file.html) to another (our_file.html?this is a test). Here's a script that we could use for that purpose. It must be put immediately before the closing body tag of the page (here: our_file.html)
<script>
var data=location.search;
if(data)
{
data = location.search.substring(1); // needed to remove the '?'
//do something with the data
data=''
}
</script>

In the above script, we can replace //do something with the data with some concrete javascript line using the variable data, like document.write(data) - or, if we want the data to be readable: document.write(unescape(data)). The result we be that a text string (this is a test) is passed from our_file.html to our_file.html?this is a test when we click on our link in our_file.html (where the link is provided by <a onclick="location.search='this is a test'">test</a>, see above).

A more interesting example of passing data from one page to another using the search portion of a URL is the following, which assumes that (i) we have an iframe in our_file.html: <iframe name="ifr" style="position: absolute; width: 300px; height: 300px; background: white" src="some_page.html"></iframe> and that (ii) //do something with the data in the script above is replaced with ifr.location.replace(data). If we now replace our original link in our_file.html with <a onclick="location.search='some_other_page.html'">some other page</a>, a click on the new link will take us to a new page our_file.html?some_other_page.html which is identical to our_file.html except for the content of the iframe, which loads some_other_page.html (in our_file.html?some_other_page.html). Of course, in order for this to work, we must create two pages some_page.html and some_other_page.html first.

This demonstrates that location.search can be used to (i) preserve the content of a given page (here: our_file.html) and, at the same time, to (ii) change the content of an iframe contained in it while going from one page to another page (here: our_file.html?some_other_page.html). So a navigation menu in the 'main page' (here: our_file.html) will be visible on all pages of a site constructed along the lines given here.
IMPORTANT: <a onclick="location.search='some_other_page.html'">some other page</a> was used above in a non-iframed page to go from some_page.html (in an iframe) to some_other_page.html (in an iframe). If we want to change the iframe's content from within the iframe, we should do <a onclick="parent.location.search='some_other_page.html'">some other page</a>.

Demo and explanations here. The demo contains features that have nothing to do with location.search, because I already used the files of the demo for another purpose. But I think it explains rather what I want to show.

Arie.