How can I get query string values in JavaScript?

This will parse variables AND arrays from a URL string. It uses neither regex or any external library.

function url2json(url) {
   var obj={};
   function arr_vals(arr){
      if (arr.indexOf(',') > 1){
         var vals = arr.slice(1, -1).split(',');
         var arr = [];
         for (var i = 0; i < vals.length; i++)
            arr[i]=vals[i];
         return arr;
      }
      else
         return arr.slice(1, -1);
   }
   function eval_var(avar){
      if (!avar[1])
          obj[avar[0]] = '';
      else
      if (avar[1].indexOf('[') == 0)
         obj[avar[0]] = arr_vals(avar[1]);
      else
         obj[avar[0]] = avar[1];
   }
   if (url.indexOf('?') > -1){
      var params = url.split('?')[1];
      if(params.indexOf('&') > 2){
         var vars = params.split('&');
         for (var i in vars)
            eval_var(vars[i].split('='));
      }
      else
         eval_var(params.split('='));
   }
   return obj;
}

Example:

var url = "http://www.x.com?luckyNums=[31,21,6]&name=John&favFoods=[pizza]&noVal"
console.log(url2json(url));

Output:

[object]
   noVal: ""
   favFoods: "pizza"
   name:     "John"
   luckyNums:
      0: "31"
      1: "21"
      2: "6"

The shortest possible expression in terms of size to obtain a query object seems to be:

var params = {};
location.search.substr(1).replace(/([^&=]*)=([^&]*)&?/g,
  function () { params[decodeURIComponent(arguments[1])] = decodeURIComponent(arguments[2]); });

You can make use of the A element to parse a URI from a string into its location-like components (to get rid of #..., for example):

var a = document.createElement('a');
a.href = url;
// Parse a.search.substr(1)... as above

This will work... You need to call this function where you need get the parameter by passing its name...

function getParameterByName(name)
{
  name = name.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
  var regexS = "[\\?&]"+name+"=([^&#]*)";
  var regex = new RegExp( regexS );
  var results = regex.exec( window.location.href );
  alert(results[1]);
  if (results == null)
    return "";
  else
    return results[1];
}

Quick, easy, and fast:

The function:

function getUrlVar() {
    var result = {};
    var location = window.location.href.split('#');
    var parts = location[0].replace(/[?&]+([^=&]+)=([^&]*)/gi, function(m,key,value) {
        result [key] = value;
    });
    return result;
}

Usage:

var varRequest = getUrlVar()["theUrlVarName"];

Use:

  $(document).ready(function () {
      var urlParams = {};
      (function () {
          var match,
          pl = /\+/g, // Regex for replacing addition symbol with a space
              search = /([^&=]+)=?([^&]*)/g,
              decode = function (s) {
                  return decodeURIComponent(s.replace(pl, " "));
              },
              query = window.location.search.substring(1);

          while (match = search.exec(query))
              urlParams[decode(match[1])] = decode(match[2]);
      })();
      if (urlParams["q1"] === 1) {
          return 1;
      }

Please check and let me know your comments. Also refer to How to get querystring value using jQuery.

Here is String prototype implementation:

String.prototype.getParam = function( str ){
    str = str.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
    var regex = new RegExp( "[\\?&]*"+str+"=([^&#]*)" );    
    var results = regex.exec( this );
    if( results == null ){
        return "";
    } else {
        return results[1];
    }
}

Example call:

var status = str.getParam("status")

str can be a query string or url

I recommend Dar Lessons as a good plugin. I have worked with it fo a long time. You can also use the following code. Jus put var queryObj = {}; before document.ready and put the bellow code in the beginning of document.ready. After this code you can use queryObj["queryObjectName"] for any query object you have

var querystring = location.search.replace('?', '').split('&');
for (var i = 0; i < querystring.length; i++) {
    var name = querystring[i].split('=')[0];
    var value = querystring[i].split('=')[1];
    queryObj[name] = value;
}

Doing this reliably is more involved than one may think at first.

1. location.search, which is used in other answers, is brittle and should be avoided - for example, it returns empty if someone screws up and puts a #fragment identifier before the ?query string.
2. There are a number of ways URLs get automatically escaped in the browser, which makes decodeURIComponent pretty much mandatory, in my opinion.
3. Many query strings are generated from user input, which means assumptions about the URL content are very bad. Including very basic things like that each key is unique or even has a value.

To solve this, here is a configurable API with a healthy dose of defensive programming. Note that it can be made half the size if you are willing to hardcode some of the variables, or if the input can never include hasOwnProperty, etc.

Version 1: Returns a data object with names and values for each parameter. It effectively de-duplicates them and always respects the first one found from left-to-right.

function getQueryData(url, paramKey, pairKey, missingValue, decode) {

    var query, queryStart, fragStart, pairKeyStart, i, len, name, value, result;

    if (!url || typeof url !== 'string') {
        url = location.href; // more robust than location.search, which is flaky
    }
    if (!paramKey || typeof paramKey !== 'string') {
        paramKey = '&';
    }
    if (!pairKey || typeof pairKey !== 'string') {
        pairKey = '=';
    }
    // when you do not explicitly tell the API...
    if (arguments.length < 5) {
        // it will unescape parameter keys and values by default...
        decode = true;
    }

    queryStart = url.indexOf('?');
    if (queryStart >= 0) {
        // grab everything after the very first ? question mark...
        query = url.substring(queryStart + 1);
    } else {
        // assume the input is already parameter data...
        query = url;
    }
    // remove fragment identifiers...
    fragStart = query.indexOf('#');
    if (fragStart >= 0) {
        // remove everything after the first # hash mark...
        query = query.substring(0, fragStart);
    }
    // make sure at this point we have enough material to do something useful...
    if (query.indexOf(paramKey) >= 0 || query.indexOf(pairKey) >= 0) {
        // we no longer need the whole query, so get the parameters...
        query = query.split(paramKey);
        result = {};
        // loop through the parameters...
        for (i = 0, len = query.length; i < len; i = i + 1) {
            pairKeyStart = query[i].indexOf(pairKey);
            if (pairKeyStart >= 0) {
                name = query[i].substring(0, pairKeyStart);
            } else {
                name = query[i];
            }
            // only continue for non-empty names that we have not seen before...
            if (name && !Object.prototype.hasOwnProperty.call(result, name)) {
                if (decode) {
                    // unescape characters with special meaning like ? and #
                    name = decodeURIComponent(name);
                }
                if (pairKeyStart >= 0) {
                    value = query[i].substring(pairKeyStart + 1);
                    if (value) {
                        if (decode) {
                            value = decodeURIComponent(value);
                        }
                    } else {
                        value = missingValue;
                    }
                } else {
                    value = missingValue;
                }
                result[name] = value;
            }
        }
        return result;
    }
}

Version 2: Returns a data map object with two identical length arrays, one for names and one for values, with an index for each parameter. This one supports duplicate names and intentionally does not de-duplicate them, because that is probably why you would want to use this format.

function getQueryData(url, paramKey, pairKey, missingValue, decode) {

   var query, queryStart, fragStart, pairKeyStart, i, len, name, value, result;

   if (!url || typeof url !== 'string') {
       url = location.href; // more robust than location.search, which is flaky
   }
   if (!paramKey || typeof paramKey !== 'string') {
       paramKey = '&';
   }
   if (!pairKey || typeof pairKey !== 'string') {
       pairKey = '=';
   }
   // when you do not explicitly tell the API...
   if (arguments.length < 5) {
       // it will unescape parameter keys and values by default...
       decode = true;
   }

   queryStart = url.indexOf('?');
   if (queryStart >= 0) {
       // grab everything after the very first ? question mark...
       query = url.substring(queryStart + 1);
   } else {
       // assume the input is already parameter data...
       query = url;
   }
   // remove fragment identifiers...
   fragStart = query.indexOf('#');
   if (fragStart >= 0) {
       // remove everything after the first # hash mark...
       query = query.substring(0, fragStart);
   }
   // make sure at this point we have enough material to do something useful...
   if (query.indexOf(paramKey) >= 0 || query.indexOf(pairKey) >= 0) {
       // we no longer need the whole query, so get the parameters...
       query = query.split(paramKey);
       result = {
           names: [],
           values: []
       };
       // loop through the parameters...
       for (i = 0, len = query.length; i < len; i = i + 1) {
           pairKeyStart = query[i].indexOf(pairKey);
           if (pairKeyStart >= 0) {
               name = query[i].substring(0, pairKeyStart);
           } else {
               name = query[i];
           }
           // only continue for non-empty names...
           if (name) {
               if (decode) {
                   // unescape characters with special meaning like ? and #
                   name = decodeURIComponent(name);
               }
               if (pairKeyStart >= 0) {
                   value = query[i].substring(pairKeyStart + 1);
                   if (value) {
                       if (decode) {
                           value = decodeURIComponent(value);
                       }
                   } else {
                       value = missingValue;
                   }
               } else {
                   value = missingValue;
               }
               result.names.push(name);
               result.values.push(value);
           }
       }
       return result;
   }

}

// Parse query string
var params = {}, queryString = location.hash.substring(1),
    regex = /([^&=]+)=([^&]*)/g,
    m;
while (m = regex.exec(queryString)) {
    params[decodeURIComponent(m[1])] = decodeURIComponent(m[2]);
}

This function will return a parsed JavaScript object with any arbitrarily nested values using recursion as necessary.

Here's a jsfiddle example.

[
  '?a=a',
  '&b=a',
  '&b=b',
  '&c[]=a',
  '&c[]=b',
  '&d[a]=a',
  '&d[a]=x',
  '&e[a][]=a',
  '&e[a][]=b',
  '&f[a][b]=a',
  '&f[a][b]=x',
  '&g[a][b][]=a',
  '&g[a][b][]=b',
  '&h=%2B+%25',
  '&i[aa=b',
  '&i[]=b',
  '&j=',
  '&k',
  '&=l',
  '&abc=foo',
  '&def=%5Basf%5D',
  '&ghi=[j%3Dkl]',
  '&xy%3Dz=5',
  '&foo=b%3Dar',
  '&xy%5Bz=5'
].join('');

Given any of the above test examples.

var qs = function(a) {
  var b, c, e;
  b = {};
  c = function(d) {
    return d && decodeURIComponent(d.replace(/\+/g, " "));
  };
  e = function(f, g, h) {
    var i, j, k, l;
    h = h ? h : null;
    i = /(.+?)\[(.+?)?\](.+)?/g.exec(g);
    if (i) {
      [j, k, l] = [i[1], i[2], i[3]]
      if (k === void 0) {
        if (f[j] === void 0) {
          f[j] = [];
        }
        f[j].push(h);
      } else {
        if (typeof f[j] !== "object") {
          f[j] = {};
        }
        if (l) {
          e(f[j], k + l, h);
        } else {
          e(f[j], k, h);
        }
      }
    } else {
      if (f.hasOwnProperty(g)) {
        if (Array.isArray(f[g])) {
          f[g].push(h);
        } else {
          f[g] = [].concat.apply([f[g]], [h]);
        }
      } else {
        f[g] = h;
      }
      return f[g];
    }
  };
  a.replace(/^(\?|#)/, "").replace(/([^#&=?]+)?=?([^&=]+)?/g, function(m, n, o) {
    n && e(b, c(n), c(o));
  });
  return b;
};

A simple solution with plain JavaScript and regular expressions:

alert(getQueryString("p2"));

function getQueryString (Param) {
    return decodeURI("http://www.example.com/?p1=p11&p2=p2222".replace(new RegExp("^(?:.*[&?]" + encodeURI(Param).replace(/[.+*]/g, "$&") + "(?:=([^&]*))?)?.*$", "i"), "$1"));
}

JsFiddle

See this post or use this:

<script type="text/javascript" language="javascript">
    $(document).ready(function()
    {
        var urlParams = {};
        (function ()
        {
            var match,
            pl= /\+/g,  // Regular expression for replacing addition symbol with a space
            search = /([^&=]+)=?([^&]*)/g,
            decode = function (s) { return decodeURIComponent(s.replace(pl, " ")); },
            query  = window.location.search.substring(1);

            while (match = search.exec(query))
                urlParams[decode(match[1])] = decode(match[2]);
        })();

        if (urlParams["q1"] === 1)
        {
            return 1;
        }
    });
</script>

This didn't work for me, I want to match ?b as the b parameter is present, and not match ?return as the r parameter, here is my solution.

window.query_param = function(name) {
  var param_value, params;

  params = location.search.replace(/^\?/, '');
  params = _.map(params.split('&'), function(s) {
    return s.split('=');
  });

  param_value = _.select(params, function(s) {
    return s.first === name;
  })[0];

  if (param_value) {
    return decodeURIComponent(param_value[1] || '');
  } else {
    return null;
  }
};