Variable by URL on all page links

Question

I am using the following code to pass variables through the URL, in wordpress.

if (isset($_GET['layout'])) {
    $layout = $_GET['layout'];
} else {
    $layout = '1';
}

With $layout I recover the value in the code, where I use to change the layout style.

By calling this url everything works very well. localhost/wp/? layout=2

In this url there are several links to other posts, pages, categories, etc. I would like that when calling a variable in the URL, the same applies to all links on that page.

For example: i start calling the variable layout at the url thus: localhost/wp/? layout=2

And on this page you will have a link to the "about" page: thus: localhost/wp/about

I wanted the variable layout be automatically placed on it and all other links.

That way: localhost/wp/about/? layout=2, localhost/wp/other-page/? layout=2, localhost/wp/category/technology/? layout=2

Answer 1

With PHP I find it difficult to do this. But with Javascript you can change all links.

The code below checks if the variable layout exists in the URL. If it exists, add it and its value to all links <a> page:

var url_ = new URL(location.href),
    var_ = url_.searchParams.get("layout");
if(var_){
   var a_ = document.body.querySelectorAll("a");
   for(var x=0; x<a_.length; x++){
      a_[x].href += (a_[x].href.indexOf("?") == -1 ? "?" : "&")+"layout="+var_;
   }
}

As the method searchParams no support in IE, follows an alternative form:

var url_ = location.href,
    param = url_.indexOf("layout");
if(param != -1){
   var var_ = url_.substring(param+7,url_.length).match(/^(\d|\w){1,}/)[0],
       a_ = document.body.querySelectorAll("a");
   for(var x=0; x<a_.length; x++){
      a_[x].href += (a_[x].href.indexOf("?") == -1 ? "?" : "&")+"layout="+var_;
   }
}

Edit

To check multiple variables and apply to links, you can insert in an array the names you want to manipulate:

var url_ = location.href,
    param = url_.substring(url_.lastIndexOf("/"), url_.length),
    params = ['layout','teste']; // insira aqui os nomes das variáveis
for(var y=0; y<params.length; y++){
   if(param.indexOf(params[y]) != -1){
      var var_ = url_.substring(url_.indexOf(params[y])+params[y].length+1,url_.length).match(/^(\d|\w){1,}/)[0],
          a_ = document.body.querySelectorAll("a");
      for(var x=0; x<a_.length; x++){
         a_[x].href += (a_[x].href.indexOf("?") == -1 ? "?" : "&")+params[y]+"="+var_;
      }
   }
}