Trying to pass variable from JavaScript to PHP using Ajax but got error " Undefined array key&q-CodePudding

I have had this error for multiple days now, I have tried searching this error up but whenever I search this error up it gives a different reason for the error and when I try to add what other sites say it doesn't work which is why I am asking here as I don't see what else I can do.

I am trying to pass a variable from JavaScript to PHP but it is not working and I have no idea why.

Here is my JavaScript code:

<head>
<script type="text/javascript" src="jquery.js"> </script>
</head>

<script>
var variable = "hello";
console.log(variable);
$.ajax
    ({
        url: "ajax.php",
        type: "POST",
        data:{pass : variable},
        success: function() { 
              alert("Success"); 
        } 
    });

</script>

Here is my PHP code:

$variable = $_POST['pass'];
echo($variable);

Everything seems to work perfectly. It writes the variable to the console, it comes up with the alert saying success. However I get an error message saying: 'Undefined array key "pass"'

What is causing this? Thank you?

CodePudding user response：

Your front end code looks OK, but I don't know your target PHP environement, but maybe your environnement doesn't accept formData.

By default, jQuery send ajax POST data as formData.

Try to send data as JSON

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

And then you will probably have to adapt your php code:

$json = file_get_contents('php://input');
// Converts it into a PHP array
$data = json_decode($json, true);
$variable = $data['pass'];
echo($variable);

CodePudding user response：

Can you please use the developer tools in chrome browser that will help you to find if data is properly sent to php file. Also you can try $_REQUEST instead of post just to check what data is coming in REQUEST as it works for GET & POST both. If it still does not help you.

Also can you please use

data: {'pass':variable}

instead of

data: {pass:variable}

let me know if it works for you.