The $.param( ) inverse function in JavaScript / jQuery

Given the following form:

<form>
    <input name="foo" value="bar">
    <input name="hello" value="hello world">
</form>

I can use the $.param( .. ) construct to serialize the form:

$.param( $('form input') )

=> foo=bar&hello=hello+world

How can I deserialize the above String with JavaScript and get a hash back?

For example,

$.magicFunction("foo=bar&hello=hello+world")

=> {'foo' : 'bar', 'hello' : 'hello world'}

Reference: jQuery.param( obj ).

You should use jQuery BBQ's deparam function. It's well-tested and documented.

This is a slightly modified version of a function I wrote a while ago to do something similar.

var QueryStringToHash = function QueryStringToHash  (query) {
  var query_string = {};
  var vars = query.split("&");
  for (var i=0;i<vars.length;i++) {
    var pair = vars[i].split("=");
    pair[0] = decodeURIComponent(pair[0]);
    pair[1] = decodeURIComponent(pair[1]);
		// If first entry with this name
    if (typeof query_string[pair[0]] === "undefined") {
      query_string[pair[0]] = pair[1];
		// If second entry with this name
    } else if (typeof query_string[pair[0]] === "string") {
      var arr = [ query_string[pair[0]], pair[1] ];
      query_string[pair[0]] = arr;
		// If third or later entry with this name
    } else {
      query_string[pair[0]].push(pair[1]);
    }
  } 
  return query_string;
};

How about this short functional approach?

function parseParams(str) {
    return str.split('&').reduce(function (params, param) {
        var paramSplit = param.split('=').map(function (value) {
            return decodeURIComponent(value.replace(/\+/g, ' '));
        });
        params[paramSplit[0]] = paramSplit[1];
        return params;
    }, {});
}

Example:

parseParams("this=is&just=an&example") // Object {this: "is", just: "an", example: undefined}

My answer:

function(query){
  var setValue = function(root, path, value){
    if(path.length > 1){
      var dir = path.shift();
      if( typeof root[dir] == 'undefined' ){
        root[dir] = path[0] == '' ? [] : {};
      }
    
      arguments.callee(root[dir], path, value);
    }else{
      if( root instanceof Array ){
        root.push(value);
      }else{
        root[path] = value;
      }
    }
  };
  var nvp = query.split('&');
  var data = {};
  for( var i = 0 ; i < nvp.length ; i++ ){
    var pair = nvp[i].split('=');
    var name = decodeURIComponent(pair[0]);
    var value = decodeURIComponent(pair[1]);

    var path = name.match(/(^[^\[]+)(\[.*\]$)?/);
    var first = path[1];
    if(path[2]){
      //case of 'array[level1]' || 'array[level1][level2]'
      path = path[2].match(/(?=\[(.*)\]$)/)[1].split('][')
    }else{
      //case of 'name'
      path = [];
    }
    path.unshift(first);

    setValue(data, path, value);
  }
  return data;
}

I am using David Dorward's answer, and realized that it doesn't behave like PHP or Ruby on Rails how they parse the params:

1. a variable is only an array if it ends with [], such as ?choice[]=1&choice[]=12, not when it is ?a=1&a=2

2. when mulitple params exist with the same name, the later ones replaces the earlier ones, as on PHP servers (Ruby on Rails keep the first one and ignore the later ones), such as ?a=1&b=2&a=3

So modifying David's version, I have:

function QueryStringToHash(query) {

  if (query == '') return null;

  var hash = {};

  var vars = query.split("&");
  
  for (var i = 0; i < vars.length; i++) {
    var pair = vars[i].split("=");
    var k = decodeURIComponent(pair[0]);
    var v = decodeURIComponent(pair[1]);

    // If it is the first entry with this name
    if (typeof hash[k] === "undefined") {

      if (k.substr(k.length-2) != '[]')  // not end with []. cannot use negative index as IE doesn't understand it
        hash[k] = v;
      else
        hash[k.substr(0, k.length-2)] = [v];

    // If subsequent entry with this name and not array
    } else if (typeof hash[k] === "string") {
      hash[k] = v;  // replace it

    // If subsequent entry with this name and is array
    } else {
      hash[k.substr(0, k.length-2)].push(v);
    }
  } 
  return hash;
};

which is tested fairly thoroughly.

I know this is an old thread, but maybe there is still some relevance in it?

Inspired by Jacky Li's good solution I tried a slight variation of my own with the objective to also be able to take care of arbitrary combinations of arrays and objects as input. I looked at how PHP would have done it and tried to get something "similar" going. Here is my code:

function getargs(str){
   var ret={};
   function build(urlnam,urlval,obj){ // extend the return object ...
    var i,k,o=obj, x, rx=/\[([^\]]*)\]/g, idx=[urlnam.replace(rx,'')];
    while (x=rx.exec(urlnam)) idx.push(x[1]); 
    while(true){
     k=idx.shift();
     if(k.trim()=='') {// key is empty: autoincremented index
       if (o.constructor.name=='Array') k=o.length; // for Array
       else if (o===obj ) {k=null}  // for first level property name
       else {k=-1;                                  // for Object
         for(i in o) if (+i>k) k=+i;
         k++;
       }
     }
     if(idx.length) { 
       // set up an array if the next key (idx[0]) appears to be
       // numeric or empty, otherwise set up an object:
       if (o[k]==null || typeof o[k]!='object') o[k]=isNaN(idx[0])?{}:[]; 
       o=o[k]; // move on to the next level
     }
     else { // OK, time to store the urlval in its chosen place ...
       // console.log('key',k,'val',urlval);                 
       o[k]=urlval===""?null:urlval; break; // ... and leave the while loop.
     } 
    }
    return obj;
   }
   // ncnvt: is a flag that governs the conversion of
   // numeric strings into numbers
   var ncnvt=true,i,k,p,v,argarr=[],
       ar=(str||window.location.search.substring(1)).split("&"),
       l=ar.length;
   for (i=0;i<l;i++) {if (ar[i]==="") continue;
     p=ar[i].split("=");k=decodeURIComponent(p[0]);
     v=p[1];v=(v!=null)?decodeURIComponent(v.replace(/\+/g,'%20')):'';
     if (ncnvt && v.trim()>"" && !isNaN(v)) v-=0;
     argarr.push([k,v]);  // array: key-value-pairs of all arguments
   }
   for (i=0,l=argarr.length;i<l;i++) build(argarr[i][0],argarr[i][1],ret);
   return ret;
}

If the function is called without the str-argument it will assume window.location.search.slice(1) as input.

Some examples:

['a=1&a=2',                               // 1 'x[y][0][z][]=1',                        // 2 'hello=[%22world%22]&world=hello',       // 3 'a=1&a=2&&b&c=3&d=&=e&',                 // 4 'fld[2][]=2&fld[][]=3&fld[3][]=4&fld[]=bb&fld[]=cc',  // 5 $.param({a:[[1,2],[3,4],{aa:'one',bb:'two'},[5,6]]}), // 6
 'a[]=hi&a[]=2&a[3][]=7&a[3][]=99&a[]=13',// 7
 'a[x]=hi&a[]=2&a[3][]=7&a[3][]=99&a[]=13'// 8
].map(function(v){return JSON.stringify(getargs(v));}).join('\n')

results in

{"a":2}                                    // 1
{"x":{"y":[{"z":[1]}]}}                    // 2
{"hello":"[\"world\"]","world":"hello"}    // 3
{"a":2,"b":null,"c":3,"d":null,"null":"e"} // 4 = { a: 2, b: null, c: 3, d: null, null: "e" }
{"fld":[null,null,[2],[3,4],"bb","cc"]}    // 5 
{"a":[[1,2],[3,4],{"aa":"one","bb":"two"},[5,6]]}  // 6
{"a":["hi",2,null,[7,99],13]}              // 7
{"a":{"0":2,"3":[7,99],"4":13,"x":"hi"}}   // 8

Whereas Jacky Li's solution would produce the outer container for a as a plain object

{a:{"0":["1","2"],"1":["3","4"],"2":["5","6"]}} // 6: JackyLi's output

getargs() looks at the first given index for any level to determine whether this level will be an object (non-numeric index) or an array (numeric or empty), thus resulting in the output as shown in the listing bove (no. 6).

If the current object is an array then nulls get inserted wherever necessary to represent empty positions. Arrays are always consecutively numbered and 0-based).

Note, that in the example no. 8 the "autoincrement" for empty indices still works, even though we are dealing with an object now and not an array.

As far as I have tested it, my getargs() behaves pretty much identically to Chriss Roger's great jQuery $.deparam() plugin mentioned in the accepted answer. The main difference is that getargs runs without jQuery and that it does autoincrement in objects while $.deparam() will not do that:

JSON.stringify($.deparam('a[x]=hi&a[]=2&a[3][]=7&a[3][]=99&a[]=13').a);

results in

{"3":["7","99"],"x":"hi","undefined":"13"}

In $.deparam() the index [] is interpreted as an undefined instead of an autoincremented numerical index.

Here's how you could create a new jQuery function:

jQuery.unparam = function (value) {
    var
    // Object that holds names => values.
    params = {},
    // Get query string pieces (separated by &)
    pieces = value.split('&'),
    // Temporary variables used in loop.
    pair, i, l;

    // Loop through query string pieces and assign params.
    for (i = 0, l = pieces.length; i < l; i++) {
        pair = pieces[i].split('=', 2);
        // Repeated parameters with the same name are overwritten. Parameters
        // with no value get set to boolean true.
        params[decodeURIComponent(pair[0])] = (pair.length == 2 ?
            decodeURIComponent(pair[1].replace(/\+/g, ' ')) : true);
    }

    return params;
};

Thanks to him http://james.padolsey.com/javascript/parsing-urls-with-the-dom/

Pretty easy :D

function params_unserialize(p){
var ret = {},
    seg = p.replace(/^\?/,'').split('&'),
    len = seg.length, i = 0, s;
for (;i<len;i++) {
    if (!seg[i]) { continue; }
    s = seg[i].split('=');
    ret[s[0]] = s[1];
}
return ret;}

Here's my JavaScript implementation which I use in a server-side JScript ASP Classic page (demo):

// Transforms a query string in the form x[y][0][z][]=1 into {x:{y:[{z:[1]}]}}
function parseJQueryParams(p) {
    var params = {};
    var pairs = p.split('&');
    for (var i=0; i<pairs.length; i++) {
        var pair = pairs[i].split('=');
        var indices = [];
        var name = decodeURIComponent(pair[0]),
            value = decodeURIComponent(pair[1]);

        var name = name.replace(/\[([^\]]*)\]/g, 
            function(k, idx) { indices.push(idx); return ""; });

        indices.unshift(name);
        var o = params;

        for (var j=0; j<indices.length-1; j++) {
            var idx = indices[j];
            var nextIdx = indices[j+1];
            if (!o[idx]) {
                if ((nextIdx == "") || (/^[0-9]+$/.test(nextIdx)))
                    o[idx] = [];
                else
                    o[idx] = {};
            }
            o = o[idx];
        }

        idx = indices[indices.length-1];
        if (idx == "") {
            o.push(value);
        }
        else {
            o[idx] = value;
        }
    }
    return params;
}

This is really old question, but as i have coming - other people may coming to this post, and i want to a bit refresh this theme. Today no need to make custom solutions - there is URLSearchParams interface.

var paramsString = "q=URLUtils.searchParams&topic=api";
var searchParams = new URLSearchParams(paramsString);

//Iterate the search parameters.
for (let p of searchParams) {
  console.log(p);
}

The only one limitation i know - this feature not supported in IE / Edge.

use this :

// convert query string to json object
var queryString = "cat=3&sort=1&page=1";

queryString
    .split("&")
    .forEach((item) => {
        const prop = item.split("=");
        filter[prop[0]] = prop[1];
    });

console.log(queryString);

I came up with this solution, which behaves like the .Net function HttpUtility.ParseQueryString.

In the result, the query string parameters are store in properties as lists of values, so that qsObj["param"] will be the same as calling GetValues("param") in .Net.

I hope you like it. JQuery not required.

var parseQueryString = function (querystring) {
	var qsObj = new Object();
	if (querystring) {
		var parts = querystring.replace(/\?/, "").split("&");
		var up = function (k, v) {
			var a = qsObj[k];
			if (typeof a == "undefined") {
				qsObj[k] = [v];
			}
			else if (a instanceof Array) {
				a.push(v);
			}
		};
		for (var i in parts) {
			var part = parts[i];
			var kv = part.split('=');
			if (kv.length == 1) {
				var v = decodeURIComponent(kv[0] || "");
				up(null, v);
			}
			else if (kv.length > 1) {
				var k = decodeURIComponent(kv[0] || "");
				var v = decodeURIComponent(kv[1] || "");
				up(k, v);
			}
		}
	}
	return qsObj;
};

Here is how to use it:

var qsObj = parseQueryString("a=1&a=2&&b&c=3&d=&=e&");

To preview the result in the console juste type in:

JSON.stringify(qsObj)

Output:

"{"a":["1","2"],"null":["","b",""],"c":["3"],"d":[""],"":["e"]}"

There's a beautiful one-liner over at CSS-Tricks (original source from Nicholas Ortenzio):

function getQueryParameters(str) {
	return (str || document.location.search).replace(/(^\?)/,'').split("&").map(function(n){return n = n.split("="),this[n[0]] = n[1],this}.bind({}))[0];
}

The really clever part is how it uses the anonymous function's this object, adding a key/value pair for each of the queries in the string. That said, there's some room for improvement. I've modified it a bit below, with the following changes:

1. Added handling of empty strings and non-string input.

2. Handled URI-encoded strings (%40->@, etc).

3. Removed the default use of document.location.search when the input was empty.

4. Changed the name, made it more readable, added comments.

function deparam(str) {
	// Uses an empty 'this' to build up the results internally
	function splitQuery(query) {
		query = query.split('=').map(decodeURIComponent);
		this[query[0]] = query[1];
		return this;
	}

	// Catch bad input
	if (!str || !(typeof str === 'string' || str instanceof String))
		return {};

	// Split the string, run splitQuery on each piece, and return 'this'
	var queries = str.replace(/(^\?)/,'').split('&');
	return queries.map(splitQuery.bind({}))[0];
}

This is my version in Coffeescript. Also works for url like http://localhost:4567/index.html?hello=[%22world%22]&world=hello#/home

getQueryString: (url)->
    return null if typeof url isnt 'string' or url.indexOf("http") is -1

    split = url.split "?"

    return null if split.length < 2 
    path = split[1]

    hash_pos = path.indexOf "#"
    path = path[0...hash_pos] if hash_pos isnt -1

    data = path.split "&"
    ret = {}
    for d in data
      [name, val] = d.split "=" 
      name = decodeURIComponent name
      val = decodeURIComponent val
      try 
        ret[name] = JSON.parse val
      catch error
        ret[name] = val
    return ret

Here's a simple & compact one if you only want to quickly get the parameters from a GET request:

function httpGet() {
	var a={},b,i,q=location.search.replace(/^\?/,"").split(/\&/);
	for(i in q) if(q[i]) {b=q[i].split("=");if(b[0]) a[b[0]]=
    decodeURIComponent(b[1]).replace(/\+/g," ");} return a;
}

It converts

something?aa=1&bb=2&cc=3

into an object like

{aa:1,bb:2,cc:3}

Creates a serialized representation of an array or object (can be used as URL query string for AJAX requests).

<button id='param'>GET</button> 
<div id="show"></div>
<script>
  $('#param').click(function () {
    var personObj = new Object();
    personObj.firstname = "vishal"
    personObj.lastname = "pambhar";
    document.getElementById('show').innerHTML=$.param(`personObj`));
  });
</script>
output:firstname=vishal&lastname=pambhar

answers could use a bit of jQuery elegance:

(function($) {
var re = /([^&=]+)=?([^&]*)/g;
var decodeRE = /\+/g; // Regex for replacing addition symbol with a space
var decode = function (str) {return decodeURIComponent( str.replace(decodeRE, " ") );};
$.parseParams = function(query) {
    var params = {}, e;
    while ( e = re.exec(query) ) {
        var k = decode( e[1] ), v = decode( e[2] );
        if (k.substring(k.length - 2) === '[]') {
            k = k.substring(0, k.length - 2);
            (params[k] || (params[k] = [])).push(v);
        }
        else params[k] = v;
    }
    return params;
};
})(jQuery);

fork at https://gist.github.com/956897

You can use the function .serializeArray() (Link) of jQuery itself. This function returns an array of key-value pair. Result example:

[  { name: "id", value: "1" },  { name: "version", value: "100" }]