passing a javascript variable to PHP with xmlhttprequest

Question

Im having problem Posting a javascript variable to a php file. Please would someone tell me what's going on?

// Get Cookies
var getCookies = document.cookie;
cookiearray  = getCookies.split(';');

SelectedIds = cookiearray[0];

//take key value pair 

 name = cookiearray[0].split('=')[0];
 value = cookiearray[0].split('=')[1]; // The variable(values) i want to pass

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

hr.open("POST", url, true);
var url = "page.php";

hr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
hr.onreadystatechange = function() {
    if(hr.readyState == 4 && hr.status == 200) {
        var return_data = hr.responseText;
        document.getElementById("Comp").innerHTML = return_data;
    }
}

hr.send(value); // Request - Send this variable to PHP
document.getElementById("Comp").innerHTML = "loading...";

PHP

 $test = $_POST['value'];
 print_r($test); // NULL

Thanks

i thik it's not an array you output, but string, try echo instead — paka
– paka, Commented Dec 10, 2013 at 12:26
Did you check what actual post body is sent? The line var url = "page.php" should be before url is referenced. (One line up) — marekful
– marekful, Commented Dec 10, 2013 at 12:26

Code Lღver · Accepted Answer · 2013-12-10 12:33:09Z

2

Instead of

 print_r($test);

use the echo

 echo $test;

As $test is not an array is a string value. print_r is used to print the array. that's why is given the null value.

And your send function in ajax should be like this:

hr.send("value="+value);

In the send function, the parameter that passed must be a string like this:

"name=value&anothername="+encodeURIComponent(myVar)+"&so=on"

1 Comment

Awena Over a year ago

Great! I had to add "value="+value . Thank you so much for the explanation.

jjack · Accepted Answer · 2021-08-01 10:05:17Z

I've been trying work out, for sometime, how to pass quite a long string I have formatted in javascript into php to save in a file and I think I now have the answer. At least it works for me.

The variable 'str' is passed into 'getGame' from another function after it has been formatted. I am using the 'POST' method as the string can get quite long. The code is:-

    function getGame(str){
    //Sends data to the php process "save Game".
    var test = str;
    var xhr = new XMLHttpRequest();
    xhr.open("POST", "saveGame.php", true);
    xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    
    xhr.onreadystatechange = function() {
        if (this.readyState === 4 ){
            alert(xhr.responseText);
        }
    };
    xhr.send("data="+ test); 
}

This sends the "data" to "saveGame.php where it is saved to a file as in the following code and returns a messsage in the alert dropdown.

<?php
$outputString = $_POST["data"];
$fp = fopen("C:\\xampp\\htdocs\\BowlsClub\\GamesSaved\\test26.txt","w");
if (!$fp){
    $message = "Error writing to file. Try again later!" ;
}else{
    fwrite($fp, $outputString);
    $message = "File saved!"; 
}
fclose($fp);

echo $message;
?>

This works for me and I hope it is useful to other newbies.

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