Adding a parameter to the URL with JavaScript

Thank you all for your contribution. I used annakata code and modified to also include the case where there is no query string in the url at all. Hope this would help.

function insertParam(key, value) {
        key = escape(key); value = escape(value);

        var kvp = document.location.search.substr(1).split('&');
        if (kvp == '') {
            document.location.search = '?' + key + '=' + value;
        }
        else {

            var i = kvp.length; var x; while (i--) {
                x = kvp[i].split('=');

                if (x[0] == key) {
                    x[1] = value;
                    kvp[i] = x.join('=');
                    break;
                }
            }

            if (i < 0) { kvp[kvp.length] = [key, value].join('='); }

            //this will reload the page, it's likely better to store this until finished
            document.location.search = kvp.join('&');
        }
    }

I have a 'class' that does this and here it is:

function QS(){
    this.qs = {};
    var s = location.search.replace( /^\?|#.*$/g, '' );
    if( s ) {
        var qsParts = s.split('&');
        var i, nv;
        for (i = 0; i < qsParts.length; i++) {
            nv = qsParts[i].split('=');
            this.qs[nv[0]] = nv[1];
        }
    }
}

QS.prototype.add = function( name, value ) {
    if( arguments.length == 1 && arguments[0].constructor == Object ) {
        this.addMany( arguments[0] );
        return;
    }
    this.qs[name] = value;
}

QS.prototype.addMany = function( newValues ) {
    for( nv in newValues ) {
        this.qs[nv] = newValues[nv];
    }
}

QS.prototype.remove = function( name ) {
    if( arguments.length == 1 && arguments[0].constructor == Array ) {
        this.removeMany( arguments[0] );
        return;
    }
    delete this.qs[name];
}

QS.prototype.removeMany = function( deleteNames ) {
    var i;
    for( i = 0; i < deleteNames.length; i++ ) {
        delete this.qs[deleteNames[i]];
    }
}

QS.prototype.getQueryString = function() {
    var nv, q = [];
    for( nv in this.qs ) {
        q[q.length] = nv+'='+this.qs[nv];
    }
    return q.join( '&' );
}

QS.prototype.toString = QS.prototype.getQueryString;

//examples
//instantiation
var qs = new QS;
alert( qs );

//add a sinle name/value
qs.add( 'new', 'true' );
alert( qs );

//add multiple key/values
qs.add( { x: 'X', y: 'Y' } );
alert( qs );

//remove single key
qs.remove( 'new' )
alert( qs );

//remove multiple keys
qs.remove( ['x', 'bogus'] )
alert( qs );

I have overridden the toString method so there is no need to call QS::getQueryString, you can use QS::toString or, as I have done in the examples just rely on the object being coerced into a string.

This is very simple solution. Its doesn't control parameter existence, and it doesn't change existing value. It adds your parameter to end, so you can get latest value in your back-end code.

function addParameterToURL(param){
    _url = location.href;
    _url += (_url.split('?')[1] ? '&':'?') + param;
    return _url;
}

Here's a vastly simplified version, making tradeoffs for legibility and fewer lines of code instead of micro-optimized performance (and we're talking about a few miliseconds difference, realistically... due to the nature of this (operating on the current document's location), this will most likely be ran once on a page).

/**
* Add a URL parameter (or changing it if it already exists)
* @param {search} string  this is typically document.location.search
* @param {key}    string  the key to set
* @param {val}    string  value 
*/
var addUrlParam = function(search, key, val){
  var newParam = key + '=' + val,
      params = '?' + newParam;

  // If the "search" string exists, then build params from it
  if (search) {
    // Try to replace an existance instance
    params = search.replace(new RegExp('[\?&]' + key + '[^&]*'), '$1' + newParam);

    // If nothing was replaced, then add the new param to the end
    if (params === search) {
      params += '&' + newParam;
    }
  }

  return params;
};

You would then use this like so:

document.location.pathname + addUrlParam(document.location.search, 'foo', 'bar');

This was my own attempt, but I'll use the answer by annakata as it seems much cleaner:

function AddUrlParameter(sourceUrl, parameterName, parameterValue, replaceDuplicates)
{
    if ((sourceUrl == null) || (sourceUrl.length == 0)) sourceUrl = document.location.href;
    var urlParts = sourceUrl.split("?");
    var newQueryString = "";
    if (urlParts.length > 1)
    {
    	var parameters = urlParts[1].split("&");
    	for (var i=0; (i < parameters.length); i++)
    	{
    		var parameterParts = parameters[i].split("=");
    		if (!(replaceDuplicates && parameterParts[0] == parameterName))
    		{
    			if (newQueryString == "")
    				newQueryString = "?";
    			else
    				newQueryString += "&";
    			newQueryString += parameterParts[0] + "=" + parameterParts[1];
    		}
    	}
    }
    if (newQueryString == "")
    	newQueryString = "?";
    else
    	newQueryString += "&";
    newQueryString += parameterName + "=" + parameterValue;

    return urlParts[0] + newQueryString;
}

Also, I found this jQuery plugin from another post on stackoverflow, and if you need more flexibility you could use that: http://plugins.jquery.com/project/query-object

I would think the code would be (haven't tested):

return $.query.parse(sourceUrl).set(parameterName, parameterValue).toString();

Ok here I compare Two functions, one made by myself (regExp) and another one made by (annakata).

Split array:

function insertParam(key, value)
{
    key = escape(key); value = escape(value);

    var kvp = document.location.search.substr(1).split('&');

    var i=kvp.length; var x; while(i--) 
    {
        x = kvp[i].split('=');

        if (x[0]==key)
        {
                x[1] = value;
                kvp[i] = x.join('=');
                break;
        }
    }

    if(i<0) {kvp[kvp.length] = [key,value].join('=');}

    //this will reload the page, it's likely better to store this until finished
    return "&"+kvp.join('&'); 
}

Regexp method:

function addParameter(param, value)
{
    var regexp = new RegExp("(\\?|\\&)" + param + "\\=([^\\&]*)(\\&|$)");
    if (regexp.test(document.location.search)) 
        return (document.location.search.toString().replace(regexp, function(a, b, c, d)
        {
                return (b + param + "=" + value + d);
        }));
    else 
        return document.location.search+ param + "=" + value;
}

Testing case:

time1=(new Date).getTime();
for (var i=0;i<10000;i++)
{
addParameter("test","test");
}
time2=(new Date).getTime();
for (var i=0;i<10000;i++)
{
insertParam("test","test");
}

time3=(new Date).getTime();

console.log((time2-time1)+" "+(time3-time2));

It seems that even with simplest solution (when regexp use only test and do not enter .replace function) it is still slower than spliting... Well. Regexp is kinda slow but... uhh...

I like the answer of Mehmet Fatih Yıldız even he did not answer the whole question.

In the same line as his answer, I use this code:

"Its doesn't control parameter existence, and it doesn't change existing value. It adds your parameter to the end"

  /** add a parameter at the end of the URL. Manage '?'/'&', but not the existing parameters.
   *  does escape the value (but not the key)
   */
  function addParameterToURL(_url,_key,_value){
      var param = _key+'='+escape(_value);

      var sep = '&';
      if (_url.indexOf('?') < 0) {
        sep = '?';
      } else {
        var lastChar=_url.slice(-1);
        if (lastChar == '&') sep='';
        if (lastChar == '?') sep='';
      }
      _url += sep + param;

      return _url;
  }

and the tester:

  /*
  function addParameterToURL_TESTER_sub(_url,key,value){
    //log(_url);
    log(addParameterToURL(_url,key,value));
  }

  function addParameterToURL_TESTER(){
    log('-------------------');
    var _url ='www.google.com';
    addParameterToURL_TESTER_sub(_url,'key','value');
    addParameterToURL_TESTER_sub(_url,'key','Text Value');
    _url ='www.google.com?';
    addParameterToURL_TESTER_sub(_url,'key','value');
    _url ='www.google.com?A=B';
    addParameterToURL_TESTER_sub(_url,'key','value');
    _url ='www.google.com?A=B&';
    addParameterToURL_TESTER_sub(_url,'key','value');
    _url ='www.google.com?A=1&B=2';
    addParameterToURL_TESTER_sub(_url,'key','value');

  }//*/

var MyApp = new Class();

MyApp.extend({
    utility: {
        queryStringHelper: function (url) {
            var originalUrl = url;
            var newUrl = url;
            var finalUrl;
            var insertParam = function (key, value) {
                key = escape(key);
                value = escape(value);

                //The previous post had the substr strat from 1 in stead of 0!!!
                var kvp = newUrl.substr(0).split('&');

                var i = kvp.length;
                var x;
                while (i--) {
                    x = kvp[i].split('=');

                    if (x[0] == key) {
                        x[1] = value;
                        kvp[i] = x.join('=');
                        break;
                    }
                }

                if (i < 0) {
                    kvp[kvp.length] = [key, value].join('=');
                }

                finalUrl = kvp.join('&');

                return finalUrl;
            };

            this.insertParameterToQueryString = insertParam;

            this.insertParams = function (keyValues) {
                for (var keyValue in keyValues[0]) {
                    var key = keyValue;
                    var value = keyValues[0][keyValue];
                    newUrl = insertParam(key, value);
                }
                return newUrl;
            };

            return this;
        }
    }
});

May be this can be another good solution:

function addParam(url, param, value) {
     var a = document.createElement('a');
     a.href = url;
     a.search += a.search.substring(0,1) == "?" ? "&" : "?";
     a.search += encodeURIComponent(param);
     if (value)
         a.search += "=" + encodeURIComponent(value);
     return a.href;
}

url = "http://www.example.com#hashme";
newurl = addParam(url, "ciao", "1");
alert(newurl);

http://jsfiddle.net/bknE4/3/

If you're messing around with urls in links or somewhere else, you may have to take the hash into account as well. Here's a fairly simple to understand solution. Probably not the FASTEST since it uses a regex... but in 99.999% of cases, the difference really doesn't matter!

function addQueryParam( url, key, val ){
    var parts = url.match(/([^?#]+)(\?[^#]*)?(\#.*)?/);
    var url = parts[1];
    var qs = parts[2] || '';
    var hash = parts[3] || '';

    if ( !qs ) {
        return url + '?' + key + '=' + encodeURIComponent( val ) + hash;
    } else {
        var qs_parts = qs.substr(1).split("&");
        var i;
        for (i=0;i<qs_parts.length;i++) {
            var qs_pair = qs_parts[i].split("=");
            if ( qs_pair[0] == key ){
                qs_parts[ i ] = key + '=' + encodeURIComponent( val );
                break;
            }
        }
        if ( i == qs_parts.length ){
            qs_parts.push( key + '=' + encodeURIComponent( val ) );
        }
        return url + '?' + qs_parts.join('&') + hash;
    }
}

Check out https://code.google.com/p/jsuri/

Uri and query string manipulation in javascript.

This project incorporates the excellent parseUri regular expression library by Steven Levithan. You can safely parse URLs of all shapes and sizes, however invalid or hideous.

I'll have a go. I'd do something like this:

function constructQuery(newkey, newvalue) {
	// the url will be split into three pieces
	var stem = window.location.href; 
	var query = "";
	var anchor = "";

	// split off the anchor
	var anchorindex = stem.lastIndexOf("#");
	if(anchorindex != -1) {
		anchor = stem.substring(anchorindex);
		stem = stem.substring(0, anchorindex);
	}

	// split off the query
	var queryindex = stem.lastIndexOf("?");
	if(queryindex != -1) {
		query = stem.substring(queryindex+1);
		stem = stem.substring(0, queryindex+1);
	}
	else{ stem += "?"; }

	// rewrite the query
	if(query != "") {
		var parameters = query.split("&");
		var newquery = "";
		for(int i = 0; i < parameters.length; ++i) {
			var parameter = parameters[i].split("=");
			if(parameter[0] == newkey) { continue; }
			if(newquery.length > 0) { newquery += "&"; }
			newquery += parameter;
		}
		query = newquery + "&" + newkey + "=" + newvalue;
	}

	// recombine the three pieces
	return stem + query + anchor;
}

I made up this code just then so I hope I've thought through everything but I might've missed something. I don't know if it even compiles, but at least you get the idea.