[javascript] How to serialize an Object into a list of URL query parameters?

Without knowing the keys of a JavaScript Object, how can I turn something like...

var obj = {
   param1: 'something',
   param2: 'somethingelse',
   param3: 'another'
}

obj[param4] = 'yetanother';

...into...

var str = 'param1=something&param2=somethingelse&param3=another&param4=yetanother';

...?

Object.keys(obj).map(k => `${encodeURIComponent(k)}=${encodeURIComponent(obj[k])}`).join('&')

A functional approach.

var kvToParam = R.mapObjIndexed((val, key) => {_x000D_
  return '&' + key + '=' + encodeURIComponent(val);_x000D_
});_x000D_
_x000D_
var objToParams = R.compose(_x000D_
  R.replace(/^&/, '?'),_x000D_
  R.join(''),_x000D_
  R.values,_x000D_
  kvToParam_x000D_
);_x000D_
_x000D_
var o = {_x000D_
  username: 'sloughfeg9',_x000D_
  password: 'traveller'_x000D_
};_x000D_
_x000D_
console.log(objToParams(o));

<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.22.1/ramda.min.js"></script>

var str = '';

for( var name in obj ) {
    str += (name + '=' + obj[name] + '&');
}

str = str.slice(0,-1);

Give this a shot.

Example: http://jsfiddle.net/T2UWT/

An elegant one: (assuming you are running a modern browser or node)

var str = Object.keys(obj).map(function(key) {
  return key + '=' + obj[key];
}).join('&');

And the ES2017 equivalent: (thanks to Lukas)

let str = Object.entries(obj).map(([key, val]) => `${key}=${val}`).join('&');

Note: You probably want to use encodeURIComponent() if the keys/values are not URL encoded.

Object.toparams = function ObjecttoParams(obj) 
{
  var p = [];
  for (var key in obj) 
  {
    p.push(key + '=' + encodeURIComponent(obj[key]));
  }
  return p.join('&');
};

this method uses recursion to descend into object hierarchy and generate rails style params which rails interprets as embedded hashes. objToParams generates a query string with an extra ampersand on the end, and objToQuery removes the final amperseand.

 function objToQuery(obj){
  let str = objToParams(obj,'');
  return str.slice(0, str.length);
}
function   objToParams(obj, subobj){
  let str = "";

   for (let key in obj) {
     if(typeof(obj[key]) === 'object') {
       if(subobj){
         str += objToParams(obj[key], `${subobj}[${key}]`);
       } else {
         str += objToParams(obj[key], `[${key}]`);
       }

     } else {
       if(subobj){
         str += `${key}${subobj}=${obj[key]}&`;
       }else{
         str += `${key}=${obj[key]}&`;
       }
     }
   }
   return str;
 }

This one-liner also handles nested objects and JSON.stringify them as needed:

let qs = Object.entries(obj).map(([k, v]) => `${k}=${encodeURIComponent(typeof (v) === "object" ? JSON.stringify(v) : v)}`).join('&')

Just for the record and in case you have a browser supporting ES6, here's a solution with reduce:

Object.keys(obj).reduce((prev, key, i) => (
  `${prev}${i!==0?'&':''}${key}=${obj[key]}`
), '');

And here's a snippet in action!

// Just for test purposes_x000D_
let obj = {param1: 12, param2: "test"};_x000D_
_x000D_
// Actual solution_x000D_
let result = Object.keys(obj).reduce((prev, key, i) => (_x000D_
  `${prev}${i!==0?'&':''}${key}=${obj[key]}`_x000D_
), '');_x000D_
_x000D_
// Run the snippet to show what happens!_x000D_
console.log(result);

If you need a recursive function that will produce proper URL parameters based on the object given, try my Coffee-Script one.

@toParams = (params) ->
    pairs = []
    do proc = (object=params, prefix=null) ->
      for own key, value of object
        if value instanceof Array
          for el, i in value
            proc(el, if prefix? then "#{prefix}[#{key}][]" else "#{key}[]")
        else if value instanceof Object
          if prefix?
            prefix += "[#{key}]"
          else
            prefix = key
          proc(value, prefix)
        else
          pairs.push(if prefix? then "#{prefix}[#{key}]=#{value}" else "#{key}=#{value}")
    pairs.join('&')

or the JavaScript compiled...

toParams = function(params) {
  var pairs, proc;
  pairs = [];
  (proc = function(object, prefix) {
    var el, i, key, value, _results;
    if (object == null) object = params;
    if (prefix == null) prefix = null;
    _results = [];
    for (key in object) {
      if (!__hasProp.call(object, key)) continue;
      value = object[key];
      if (value instanceof Array) {
        _results.push((function() {
          var _len, _results2;
          _results2 = [];
          for (i = 0, _len = value.length; i < _len; i++) {
            el = value[i];
            _results2.push(proc(el, prefix != null ? "" + prefix + "[" + key + "][]" : "" + key + "[]"));
          }
          return _results2;
        })());
      } else if (value instanceof Object) {
        if (prefix != null) {
          prefix += "[" + key + "]";
        } else {
          prefix = key;
        }
        _results.push(proc(value, prefix));
      } else {
        _results.push(pairs.push(prefix != null ? "" + prefix + "[" + key + "]=" + value : "" + key + "=" + value));
      }
    }
    return _results;
  })();
  return pairs.join('&');
};

This will construct strings like so:

toParams({a: 'one', b: 'two', c: {x: 'eight', y: ['g','h','j'], z: {asdf: 'fdsa'}}})

"a=one&b=two&c[x]=eight&c[y][0]=g&c[y][1]=h&c[y][2]=j&c[y][z][asdf]=fdsa"

One line with no dependencies:

new URLSearchParams(obj).toString();
// OUT: param1=something&param2=somethingelse&param3=another&param4=yetanother

Use it with the URL builtin like so:

let obj = { param1: 'something', param2: 'somethingelse', param3: 'another' }
obj['param4'] = 'yetanother';
const url = new URL(`your_url.com`);
url.search = new URLSearchParams(obj);
const response = await fetch(url);

[Edit April 4, 2020]: null values will be interpreted as the string 'null'.

If you use jQuery, this is what it uses for parameterizing the options of a GET XHR request:

$.param( obj )

http://api.jquery.com/jQuery.param/

ES6:

function params(data) {_x000D_
  return Object.keys(data).map(key => `${key}=${encodeURIComponent(data[key])}`).join('&');_x000D_
}_x000D_
_x000D_
console.log(params({foo: 'bar'}));_x000D_
console.log(params({foo: 'bar', baz: 'qux$'}));

Since I made such a big deal about a recursive function, here is my own version.

function objectParametize(obj, delimeter, q) {
    var str = new Array();
    if (!delimeter) delimeter = '&';
    for (var key in obj) {
        switch (typeof obj[key]) {
            case 'string':
            case 'number':
                str[str.length] = key + '=' + obj[key];
            break;
            case 'object':
                str[str.length] = objectParametize(obj[key], delimeter);
        }
    }
    return (q === true ? '?' : '') + str.join(delimeter);
}

http://jsfiddle.net/userdude/Kk3Lz/2/

You could use npm lib query-string

const queryString = require('query-string');

querystring.stringify({ foo: 'bar', baz: ['qux', 'quux'], corge: '' });
// Returns 'foo=bar&baz=qux&baz=quux&corge='

A useful code when you have the array in your query:

var queryString = Object.keys(query).map(key => {
    if (query[key].constructor === Array) {
        var theArrSerialized = ''
        for (let singleArrIndex of query[key]) {
            theArrSerialized = theArrSerialized + key + '[]=' + singleArrIndex + '&'
        }
        return theArrSerialized
    }
    else {
        return key + '=' + query[key] + '&'
    }
}
).join('');
console.log('?' + queryString)

You can use jQuery's param method:

var obj = {_x000D_
  param1: 'something',_x000D_
  param2: 'somethingelse',_x000D_
  param3: 'another'_x000D_
}_x000D_
obj['param4'] = 'yetanother';_x000D_
var str = jQuery.param(obj);_x000D_
alert(str);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

For one level deep...

var serialiseObject = function(obj) {
    var pairs = [];
    for (var prop in obj) {
        if (!obj.hasOwnProperty(prop)) {
            continue;
        }
        pairs.push(prop + '=' + obj[prop]);
    }
    return pairs.join('&');
}

jsFiddle.

There was talk about a recursive function for arbitrarily deep objects...

var serialiseObject = function(obj) {
    var pairs = [];
    for (var prop in obj) {
        if (!obj.hasOwnProperty(prop)) {
            continue;
        }
        if (Object.prototype.toString.call(obj[prop]) == '[object Object]') {
            pairs.push(serialiseObject(obj[prop]));
            continue;
        }
        pairs.push(prop + '=' + obj[prop]);
    }
    return pairs.join('&');
}

jsFiddle.

This of course means that the nesting context is lost in the serialisation.

If the values are not URL encoded to begin with, and you intend to use them in a URL, check out JavaScript's encodeURIComponent().

If you're using NodeJS 13.1 or superior you can use the native querystring module to parse query strings.

const qs = require('querystring');
let str = qs.stringify(obj)

ES2017 approach

Object.entries(obj).map(([key, val]) => `${key}=${val}`).join('&')

With Axios and infinite depth:

<pre>
    <style>
      textarea {
        width: 80%;
        margin-bottom: 20px;
      }
      label {
        font-size: 18px;
        font-weight: bold;
      }
    </style>
    <label>URI</label>
    <textarea id="uri"  rows="7"></textarea>
    <label>All Defaults (Bonus): </label>
    <textarea id="defaults" rows="20"></textarea>
</pre>

<script src="https://unpkg.com/axios/dist/axios.min.js"></script>

<script>
  const instance = axios.create({
    baseUrl: 'http://my-api-server',
    url: '/user'
  })
  const uri = instance.getUri({
    params: {
      id: '1234',
      favFruits: [
        'banana',
        'apple',
        'strawberry'
      ],
      carConfig: {
        items: ['keys', 'laptop'],
        type: 'sedan',
        other: {
          music: ['on', 'off', {
            foo: 'bar'
          }]
        }
      }
    }
  })
  const defaults = JSON.stringify(instance.defaults, null, 2)
  document.getElementById('uri').value = uri
  document.getElementById('defaults').value = defaults
</script>

Good Luck...