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Pass a PHP string to a Javascript variable (and escape newlines)

I have several constants in a PHP application I'm developing. I've defined a Constants class and the defined the constants as const VAR_NAME = value; in this class. I would like to share these constants between my JavaScript and PHP code. Is there a DRY (Don't Repeat Yourself) mechanism to share them?

class Constants {
    const RESOURCE_TYPE_REGSITER = 2;
    const RESOURCE_TYPE_INFO = 1;
}
Community
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Brian Fisher
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4 Answers4

8

I would use json_encode. You will have to convert the class to an associative array first.

$constants = array("RESOURCE_TYPE_REGISTER"=>2, "RESOURCE_TYPE_INFO"=>2);
echo json_encode($constants);

You could also use reflection to convert the class to an associative array if you would prefer to use a class.

function get_class_consts($class_name)
{
    $c = new ReflectionClass($class_name);
    return ($c->getConstants());
}

class Constants {
    const RESOURCE_TYPE_REGSITER = 2;
    const RESOURCE_TYPE_INFO = 1;
}

echo json_encode(get_class_consts("Constants"));
Adam Peck
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  • You mixed JavaScript and PHP syntax. There is no JSON object in PHP. There are just json_*() functions. – Gumbo Jan 13 '09 at 20:01
  • Oops. I have updated it so there is no confusion :D – Adam Peck Jan 13 '09 at 20:04
  • This is great, however, get_class_vars seems to skip the const variables in the class. – Brian Fisher Jan 13 '09 at 20:09
  • Hey at least it's right now :) Although I still think the simplest way is to leave it in an associative array. And this time I actually tested it too! – Adam Peck Jan 13 '09 at 20:29
  • Thanks, this works great. I like using the const member variables instead of an associative array, because my IDE can then do code completion. – Brian Fisher Jan 13 '09 at 21:25
2

Put a list of constants common to both JavaScript and PHP in "client_server_shared.js".

'var' is required in JavaScript, and is legal (though deprecated) in PHP if inside a class. '$' to start a variable name is required in PHP, and legal in JavaScript.

var $shared_CONSTANT1 = 100;
var $shared_CONSTANT2 = 'hey';

PHP Code:

eval('class Client_server_shared{'                   ."\n"
.     file_get_contents( 'client_server_shared.js' ) ."\n"
.    '}'
.    '$client_server = new Client_server_shared();'
);

echo $client_server->shared_CONSTANT1;   // Proof it works in PHP.
echo $client_server->shared_CONSTANT2;

JavaScript Code:

alert( $shared_CONSTANT1 );              // Proof it works in JavaScript.
alert( $shared_CONSTANT2 );
Dave
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    I really like the simplicity of this solution, but if var is deprecated in PHP, we should assume this solution will eventually break, right? – skelliam Oct 26 '17 at 13:57
-1

The only way you can share the constants is to have the php side inform the javascript. For instance: 

echo "<script> var CONSTANT1 =".$constant_instance->CONSTANT_NAME.";</script>";

Or using ajax, you could also write a small script that would return the constants as JSON/whatever.

jacobangel
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-2

A bit of an ugly hack, but here it goes:

constants.js

//<?php
$const1 = 42;
$const2 = "Hello";
//?>

constants.html (use inside JavaScript)

<script type="text/javascript" src="constants.js"></script>
<script type="text/javascript">document.write($const1);</script>

constants.php (use inside PHP)

<?php
ob_start(); // start buffering the "//"
require "constants.js";
ob_end_clean(); // discard the buffered "//"

echo $const1;
?>
Ates Goral
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