404.html
<!DOCTYPE html>
<html lang="en">
<head>
<script>
var location = window.location;
// like ?agencies=DOD,USAID&languages=Python
var search = location.search;
var pathName = location.pathname;
var newSearch;
if (search && search.length > 0 && search[0] === "?") {
newSearch = search + "&p=" + pathName;
} else {
newSearch = "?p=" + pathName;
}
// don't include the pathname (e.g. '/browse-projects')
const newUrl = location.origin + newSearch;
location.replace(newUrl);
</script>
</head>
<body>
</body>
</html>