How can I add or update a query string parameter?

Question

With javascript how can I add a query string parameter to the url if not present or if it present, update the current value? I am using jquery for my client side development

Answer 1

Based on @amateur's answer (and now incorporating the fix from @j_walker_dev comment), but taking into account the comment about hash tags in the url I use the following:

function updateQueryStringParameter(uri, key, value) {
  var re = new RegExp("([?&])" + key + "=.*?(&|#|$)", "i");
  if (uri.match(re)) {
    return uri.replace(re, '$1' + key + "=" + value + '$2');
  } else {
    var hash =  '';
    if( uri.indexOf('#') !== -1 ){
        hash = uri.replace(/.*#/, '#');
        uri = uri.replace(/#.*/, '');
    }
    var separator = uri.indexOf('?') !== -1 ? "&" : "?";    
    return uri + separator + key + "=" + value + hash;
  }
}

Edited to fix [?|&] in regex which should of course be [?&] as pointed out in the comments

Edit: Alternative version to support removing URL params as well. I have used value === undefined as the way to indicate removal. Could use value === false or even a separate input param as wanted.

function updateQueryStringParameter(uri, key, value) {
  var re = new RegExp("([?&])" + key + "=.*?(&|#|$)", "i");
  if( value === undefined ) {
    if (uri.match(re)) {
        return uri.replace(re, '$1$2');
    } else {
        return uri;
    }
  } else {
    if (uri.match(re)) {
        return uri.replace(re, '$1' + key + "=" + value + '$2');
    } else {
    var hash =  '';
    if( uri.indexOf('#') !== -1 ){
        hash = uri.replace(/.*#/, '#');
        uri = uri.replace(/#.*/, '');
    }
    var separator = uri.indexOf('?') !== -1 ? "&" : "?";    
    return uri + separator + key + "=" + value + hash;
  }
  }  
}

See it in action at https://jsfiddle.net/bp3tmuxh/1/