How do I parse a URL query parameters, in Javascript?

In Javascript, how can I get the parameters of a URL string (not the current URL)?

like:

www.domain.com/?v=123&p=hello

Can I get "v" and "p" in a JSON object?

Answer

Today (2.5 years after this answer) you can safely use Array.forEach. As @ricosrealm suggests, decodeURIComponent was used in this function.

function getJsonFromUrl(url) {
  if(!url) url = location.search;
  var query = url.substr(1);
  var result = {};

  query.split("&").forEach(function(part) {
    var item = part.split("=");
    result[item[0]] = decodeURIComponent(item[1]);
  });
  return result;
}

actually it's not that simple, see the peer-review in the comments, especially:

• hash based routing (@cmfolio)


• array parameters (@user2368055)


• proper use of decodeURIComponent (@AndrewF)

Maybe this should go to codereview SE, but here is safer and regexp-free code:

function getJsonFromUrl(url) {
  if(!url) url = location.href;

  var question = url.indexOf("?");
  var hash = url.indexOf("#");
  if(hash==-1 && question==-1) return {};
  if(hash==-1) hash = url.length;
  var query = question==-1 || hash==question+1 ? url.substring(hash) : 
  url.substring(question+1,hash);
  var result = {};
  query.split("&").forEach(function(part) {
    if(!part) return;
    part = part.split("+").join(" "); // replace every + with space, regexp-free version

    var eq = part.indexOf("=");
    var key = eq>-1 ? part.substr(0,eq) : part;
    var val = eq>-1 ? decodeURIComponent(part.substr(eq+1)) : "";
    var from = key.indexOf("[");
    if(from==-1) result[decodeURIComponent(key)] = val;
    else {
      var to = key.indexOf("]",from);
      var index = decodeURIComponent(key.substring(from+1,to));
      key = decodeURIComponent(key.substring(0,from));
      if(!result[key]) result[key] = [];

      if(!index) result[key].push(val);
      else result[key][index] = val;
    }
  });
  return result;
}

I also replaced non-encoded + for space according to this article which is also useful guide how to encode adhering to RFC 3986.

Note the result[key][index] = val: a new array item is created, it is enumerable, so it can be iterated by forEach call. Therefore, you can parse even URLs like

var url = "?foo%20e[]=a%20a&foo+e[%5Bx%5D]=b&foo e[]=c";
// {"foo e": ["a a",  "c",  "[x]":"b"]}

var obj = getJsonFromUrl(url)["foo e"];
for(var key in obj) { // Array.forEach would skip string keys here
  console.log(key,":",obj[key]);
}
/*

  0 : a a
  1 : c
  [x] : b
*/