transfer a Variable from php to js

Question

I got really confused when i tried to transfer variables from php to js. everything is fine when i try to get value using an id
for example:

var name = $         


        

Answer 1

what the code does is:

<?php
    $number = rand();  //assign random number to $number. let's say it's "3"
?>

//then these are printed on the page normally
<script language="javascript">
    var num = <?php echo $number ?> //the $number is echoed at this position
</script>

and then the browser receives:

<script language="javascript">
    var num = 3;
</script>

Answer 2

Not quite. Encoding as JSON will ensure that it is a valid JavaScript literal.

var num = <?php echo json_encode($number) ?>

Answer 3

You have to generate syntactically VALID javascript. PHP can echo text into ANY part of the page it's generating, but that doesn't necessarily mean it's actually USABLE text. In your case, you've forgotten a ;, so your generated javascript is actually a syntax error:

var num = <?php echo $number ?>;
                               ^--- missing

The same sort of thing occurs when you're outputting text. Consider where you're storing someone's name into a variable:

<?php
   $name = "Miles O'Brien"; // <-- note the single quote
?>
<script>
   var name = <? php echo $name ?>;
</script>

This LOOKS ok, but it'll actually generate yet another syntax error:

    var name = Miles O'Brien;

there's no quotes around the whole string, and the embedded quote will START a string in javascript, leading the JS interpreter to complain about an undefined variable "Miles", an undfined variable "O", and an unterminated string literal.

Instead, the PHP should have been:

 var name = <? echo json_encode($name) ?>;

The JSON encapsulation guarantees that you're embedding syntactically valid Javascript values.