access javascript array from a php file

Use json. Encode array in js (How do I encode a javascript object as JSON?), decode it in php (http://php.net/manual/ro/function.json-decode.php).

If you set up the ajax call with an object for the "data" parameter:

$.ajax({
   type: "POST",
   url: "File.php", 
   beforeSend: function () {
     $("#result").html("<option>Loading ...</option>");
   },
   data: { vArray: vArray },  // here
   success: function(msg){
     $("#result").html(msg);
   }
 });

Then jQuery will create HTTP request parameters like this:

 vArray[]=first value
 vArray[]=second value

etc. On the server side, when you access

 $vArray = $_POST['vArray'];

you'll get the array back. You don't have to explicitly mess with JSON if you don't want to, in other words.

Pure javascript for modern browser (needs support for formData & xhr2)(chrome,safari,ios,android,ie10)

js

var vArray=['a','b','c'],
json=JSON.stringify(vArray);//this converts the array to a json string

function ajax(a,b,e,d,c){ //Url,callback,method,formdata or{key:val},placeholder
 c=new XMLHttpRequest;
 c.open(e||'get',a);
 c.onload=b;
 c.send(d||null)
}
function whatever(){
 console.log('json posted',this.response)
}

ajax('page.php',whatever,'post',{'json':json});

page.php

<?php
print_r(json_decode($_POST['json']));//converts the json string to a php array
?>

Another solution is to post the whole form

html

<form>
<input name="a" value="x">
<input type="radio" name="b" value="x">
//and many other input & text fields
</form>

js

function ajax(a,b,e,d,c){ //Url,callback,method,formdata or{key:val},placeholder
 c=new XMLHttpRequest;
 c.open(e||'get',a);
 c.onload=b;
 c.send(d||null)
}
function whatever(){
 console.log('form posted',this.response)
}

var form=document.getElementsByTagName('form')[0],
    fd=new FormData(form);

ajax('page.php',whatever,'post',fd);

php

<?php
print_r($_POST);
?>

xhr2

https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest

formData

https://developer.mozilla.org/en-US/docs/Web/API/FormData

I have tried the following that seems to work fine :

<script language="JavaScript" type="text/javascript">
function ajax_post(){

// Create our XMLHttpRequest object
var hr = new XMLHttpRequest();

// Create some variables we need to send to our PHP file
var url = "my_parse_file.php";
var fn = document.getElementById("first_name").value;
var ln = document.getElementById("last_name").value;
var vars = "firstname="+fn+"&lastname="+ln;
hr.open("POST", url, true);
// Set content type header information for sending url encoded variables in the request
hr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

// Access the onreadystatechange event for the XMLHttpRequest object
hr.onreadystatechange = function() {
    if(hr.readyState == 4 && hr.status == 200) {
        var return_data = hr.responseText;
        document.getElementById("status").innerHTML = return_data;
    }
}
// Send the data to PHP now... and wait for response to update the status div
hr.send(vars); // Actually execute the request
document.getElementById("status").innerHTML = "processing...";
}
</script>

It is working really well for me. Code taken from http://www.developphp.com/view.php?tid=1185

Answers by @Pointy and @Cocco might be correct, I could not manage to implement it right with Jquery, neither wanted to use a Form.. Hope this helps someone