JQuery :: Possible To Replace String Characters?

I am running a search on my web site which uses jQuery to take the search terms and build up a URL based on them. For example, if someone searches for "chair" my URL will be appended with /chair/. However, if someone searches for something which is two words, for example "chair covers" I need the space in between to be replaced by a "+" sign so the URL will now be appended with /chair+covers/ I'm not sure if it is possible to string replace in jQuery?

Here is my current code:
function sendSearchInput(whichelement,hiddeninput,formid) {
hval = $("#"+hiddeninput).val();
$("#"+formid).submit(function() {
if ($("input:#"+whichelement).val() != hval) {
var searchval = $("#"+whichelement).val().toLowerCase();
$("#"+formid).attr("action","retail/search/"+searchval+"/");
return true;
}
$("input:#"+whichelement).focus();
return false;
});}

This will basically check that the form is not the default value (specified in the hidden field "hval") and then change the search term to lowercase and append the URK using "attr". I have tried a couple of methods including
var test = searchval.text().replace(' ','+');
And then trying to alert "test" to check it but the function just simply doesn't work.