How to pass a PHP variable to Javascript?

Question

I have 2 pages, one PHP and one Javascript. I'd like to pass the variable from this PHP script on one page:

$strFind="SELECT * FROM  cometchat_chatrooms_users WHERE userid=$curmemid";
$result=mysql_query($strFind) or die(mysql_error());
$row=mysql_fetch_array($result);
$room=$row['chatroomid'];

to this Javascript on another page:

var timestamp = 0;
var currentroom = $room;
var heartbeatTimer;
var minHeartbeat = 3000;
var maxHeartbeat = 12000;

How can I do this?

Answer 1

You can do this, when the JavaScript is generated by PHP. Example given:

<?php
...
$curmemid = intval($externalValue);
$strFind = 'SELECT * FROM cometchat_chatrooms_users WHERE userid='.$curmemid;
$result = mysql_query($strFind) or die(mysql_error());

if (isset($result)) {
    $row = mysql_fetch_array($result);
    $room = $row['chatroomid'];
} else
{
    echo 'There is something wrong!';
    $room = -1;
}
...
?>
<script type="text/javascript">
var timestamp = 0;
var currentroom = <?php echo $room; ?>;
var heartbeatTimer;
var minHeartbeat = 3000;
var maxHeartbeat = 12000;
</script>

Answer 2

<?php

$strFind="SELECT * FROM  cometchat_chatrooms_users WHERE userid=$curmemid";
$result=mysql_query($strFind) or die(mysql_error());
$row=mysql_fetch_array($result);
$room=$row['chatroomid'];

?>
<script type="text/javascript">
var timestamp = 0;
var currentroom = <?php if(isset($room))echo $room; else echo ""; ?>;
var heartbeatTimer;
var minHeartbeat = 3000;
var maxHeartbeat = 12000;
</script>

Answer 3

Another option is that of PHP outputting a hidden element with the variable in it and then JS reading it.

For instance

<?php
echo '<input type="hidden" id="myvar" value='.$val.' />';
?>

and then in JS

 var v = document.getElementById("myvar");
 // do something with v.value

Of course this is easily spoofable by the client, so take 2 cautions:

1) use this only if it is not a problem for any user to be able to see the value of the variable (e.g. by looking at the source)

2) if the JS does anything that can be possibly "dangerous" e.g. does an asynchronous call to a PHP page that does something in the DB with that value, be sure to have proper checks in the second PHP page (NOT in the JS) to ensure that the value had not been tampered with

Answer 4

You cannot actually "pass" a variable anywhere. But only a scalar value. Frankly, you can pass only text data.
So, in case of javascript you have 2 options:

1. To generate whole js code from PHP along with all it's variables. Much like to how you generate HTML.

2. To request some variable from JS running in a browser, using AJAX technique.

Answer 5

for another page you can use $_SESSION

<script type="text/javascript">
var timestamp = 0;
var currentroom = <?php echo $_SESSION['room']; ?>;
var heartbeatTimer;
var minHeartbeat = 3000;
var maxHeartbeat = 12000;
</script>

For same file/script sequence- its very simple, no need of SESSION

   var currentroom = <?php echo $room; ?>;

Answer 6

try to use Session to store your room variable and use it with javascript by the echo instruction

Answer 7

The code will work as is. When the output (html and javascript) is generated by your php it will already have done the substitution. So your value will be inserted there as a literal. If it is a string, you'll still have to quote it though.

var currentroom = '$room';

will become

var currentroom = 'myroom';

in output.