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This question already has an answer here:

I have the following function and I am wanting to assign the variable "Quantity" to php variable using Ajax but, I am not don't know much about ajax so can someone please give me the code that will do the job. Thanks

var Quantity;
$("select").change(function() {
  var str = "";
  var price = <?php echo $row[price];?>;
  $("select option:selected").each(function() {
    str += $(this).text() + " ";
  });
  $(".plan_price").text("price : " + parseInt(str) * price + " baht");
  Quantity = parseInt(str);
}).change();

function selectOne() {
  var select = document.getElementById('quantity');
  for (var i=0; i<<?php echo $row[item_amount]?>; i++) {
    select.options[select.options.length] = new Option(i+1, i);
  } 
}

I want the quantity variable to be subtracted from the $row[item_amount] from the server

if ($row[item_amount] - Quantity  == 0) {
   $sql = "update item set active='2',item_amount=item_amount-Quantity,buy_time=NOW() where id='$id'";
} else {
   $sql = "update item set item_amount=item_amount-Quantity,buy_time=NOW() where id='$id'";
}
$result = mysql_query($sql);
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2  
Java is not JavaScript. – Luiggi Mendoza Apr 29 at 0:09
google about javascript & POST method – Jirka Kopřiva Apr 29 at 0:11
I've found the best way is to separate HTML/JS/CSS from your PHP. I do not generate "code" from my php. I use php as a "data source" for ajaxing. Code should be static, I have yet to find a reason code should be dynamic (other than plugins), other than to "impress" someone. – Jeremy Walton Apr 29 at 0:55

marked as duplicate by Marc B, hjpotter92, CloudyMarble, Eelke, tkanzakic Apr 29 at 6:29

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

2 Answers

up vote 0 down vote

add this:

on your javascript:

...
Quantity = parseInt(str);
$.ajax({url:"yourphp.php",type:"POST",async:false,data:{quantity:Quantity}});

on your PHP:

...
$Quantity = $_POST["quantity"];
if ($row[item_amount] - $Quantity  == 0) {

I dont know if the "Quantity" in your mysql queries refers to $Quantity that sent by javascript; if yes, add there also the $ prefix.

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up vote 0 down vote

There are ways. You can use PHP session variables to do this. You can use the snippet below to save a take a POST variable and save it as a PHP session variable.

<?php

header('Content-Type: application/json; charset=UTF-8');

session_start();

if ($_POST['foo'] == true) {
  $_SESSION['foo'] = $_POST['foo'];
  echo json_encode(true);
}
else {
  echo json_encode(false);
}

?>

Now you need your JavaScript to connect to the PHP script and, it looks like you're using jQuery already, so we'll do it like this:

$.post('/_/ajax/init_session.php', { foo: 'bar' }, function(data) {
  console.log(data);
}, json);

The JS snippet above asks the PHP script to save $_SESSION['foo'] as 'bar'. When the data has been received, your browser's JavaScript console displays either true or false, depending on if the value has been saved or not.

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