I'm assuming you're making a POST request with a JSON payload. First, you want to make sure your payload is formatted JSON correctly, use: http://pro.jsonlint.com/

Secondly, you can send the payload using JSON.stringify and you will want to set the contentType:

data: JSON.stringify(data), contentType: "application/json; charset=utf-8"

If you run this and look at your network tab in Dev Tools in Chrome, it will error out, but you will at least see the payload formatted to send to the server: http://prntscr.com/f8hf6s

var data = [{
    "key": "myKey",
    "keyName": "myKeyName",
    "value": "value",
    "valueName": "valueName"
  },
  {
    "key": "mySecondKey",
    "keyName": "mySecondKeyName",
    "value": "secondValue",
    "valueName": "secondValueName"
  }
];

var url = "http://swapi.co/api/";

$.ajax({
  type: "POST",
  url: url,
  data: JSON.stringify(data),
  contentType: "application/json; charset=utf-8",
  dataType: "json",
  error: function() {
    alert("Error");
  },
  success: function() {
    alert("OK");
  }
});

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

In JavaScript / JSON arrays are 0 based indexed data structures. What you are using here is more like a Map:

var jsonArray = [];
jsonArray["company_name"]=company_name ;

In JavaScript you cannot use arrays like this (well you can, but it is probably not what you want). For a data structure like a map that maps strings to objects rather then an index to objects, just use an object.

Or in short: Use var jsonArray = {}; rather than var jsonArray = []; The {} will create an object that you can assign properties to like you did. And JSON.stringify will correctly translate this into a JSON string like this:

{ "property": value, "otherProperty", otherValue }

As mentioned, use serializeArray(). To add your extra parameter, just append it to the array as shown below.

function setupForm(){
    $("#add").submit(function(event) {
        event.preventDefault();

        var data = $(this).serializeArray();
            // add extra parameters (don't forget brackets)
            data.push({ name: 'loc[]', value: 44 });
            data.push({ name: 'loc[]', value: 44 });

        $.ajax({
            type: "POST",
            url: "http://localhost:3000/services",
            data: data,
            success: function() {
               alert('success');
            }
        });
    });
}

If you want to continue using your method of just building the query string, you would have to add &loc[]=44&loc[]=44 but it is better in the long run to just use one of the serialize functions.

That's not how POST request works. Read more about Ajax, but for now, that's how you should do it.

var songlist = ['song1', 'song2', 'song3'];

var sendData = function() {
  $.post('test.php', {
    data: songlist
  }, function(response) {
    console.log(response);
  });
}
sendData();

// test.php
<?php
$songData = $_POST['data'];
print_r($songData);
?>

If you want to pass a JavaScript object/hash (ie. an associative array in PHP) then you would do:

$.post('/url/to/page', {'key1': 'value', 'key2': 'value'});

If you wanna pass an actual array (ie. an indexed array in PHP) then you can do:

$.post('/url/to/page', {'someKeyName': ['value','value']});

If you want to pass a JavaScript array then you can do:

$.post('/url/to/page', {'someKeyName': variableName});

This line:

JSON.stringify(object);

does nothing useful: you're throwing away the returned value from JSON.stringify(). Instead:

object = JSON.stringify(object);

will keep it around.

You really should be encoding your parameters too:

xmlhttp.send("json=" + encodeURIComponent(object) + "&uid=" + encodeURIComponent(uid));

You firstly need to encode your array in Javascript, like so:

var options = JSON.stringify(['foo', 'bar']);

$.post('index.php?option=component&view=componentview&Itemid=123&tmpl=component&layout=xlsx&options=' + options);

Then in your PHP code, use the following instead of $_POST:

$input = JFactory::getApplication()->input;
$xlsx  = json_decode($input->get('xlsx_options'));

echo $xlsx->foo;
echo $xlsx->bar;

I generally use $.ajax for this purpose but since you have asked not to use jquery, so in that case you need to make XHR Request to the endpoint specified in you node application.

Client Side

var xmlhttp;

if (window.XMLHttpRequest) {

    // code for IE7+, Firefox, Chrome, Opera, Safari
    xmlhttp = new XMLHttpRequest();
}

else {
    // code for IE6, IE5
    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}

xmlhttp.onreadystatechange = function() {
    if (xmlhttp.readyState == XMLHttpRequest.DONE ) {
       if(xmlhttp.status == 200){
           console.log('request successfull : ', xmlhttp.responseText);
       }
       else if(xmlhttp.status == 400) {
          alert('There was an error 400')
       }
       else {
           alert('something else other than 200 was returned')
       }
    }
}

xmlhttp.open("post", "~/process_post", true);
xmlhttp.send(JSON.stringify(..........)); //your custom data

Server Side Node

app.post('/process_post', urlencodedParser, function (req, res) { 
    console.log("Got request: " + res.body);
});

Just looking for some another question already asked on Stackoverflow, I find this useful for you.

The data attribute should be an object.

What you can do is this:

$.ajax({
  url: 'http://something.com/ajax',
  data: {schedule: schedule},
  type: 'POST'
});

So if you receive this for example in PHP you have $_POST["schedule"]. An that is exactly the same as you had in JavaScript.

Ohh yes I've forgot... also have a look at .serialize() and .serializeArray()!

You can do JSON.stringify(). This will convert your array into a string, which can be passed across the network via GET or POST. In the node server, you can parse this string and get the array using JSON.parse. Adding a working Example below

var Coordinates = [
      {lat: 37.772, lng: -122.214},
      {lat: 21.291, lng: -157.821},
      {lat: -18.142, lng: 178.431},
      {lat: -27.467, lng: 153.027}
                              ];

var a = JSON.stringify(Coordinates)
console.log('Coordinates string: ', a)

var parsed = JSON.parse(a)
console.log('Parsed Coordinates: ', parsed)