PHP constant inside JS file

Question

I am facing a problem that I can not understand .

During a plugin development I am including a file.js.php (register/enqueue).

<?
/* 
File.js.php
*/
Header("content-type: application/javascript");
$path =  constant('WP_PLUGIN_DIR'); //test with function
$path_2 =  WP_PLUGIN_DIR; // test directly
//can cause a problem with older browsers?? use text/javascript
?>
//////////////////// Begin Tests  ////////////
var templateDir = "<?php echo WP_PLUGIN_URL ?>" ;
var templateDir2 = "<?php echo $path ?>" ;
var templateDir3 = "<?php echo $path_2 ?>" ;
var templateDir4 = "<?php echo constant("WP_PLUGIN_URL") ?>";
var templateDir5 = "<?php echo __FILE__ ?>";
var templateDir6 = "<?php echo plugins_url( 'somedir/somefile.png' , dirname(__FILE__)) ?>";

Results :

var templateDir = "WP_PLUGIN_URL" ; // simply outputs a string of the constant name
var templateDir2 = "" ; // null or empty
var templateDir3 = "WP_PLUGIN_DIR" ;// simply outputs a string of the constant name
var templateDir4 = "//Warning:  constant()  Couldn't find constant WP_PLUGIN_URL in .."
var templateDir5 = "path.to.js.php" // only one that works ;
var templateDir6 = "Call to undefined function  plugins_url() in.. "

so my tests showed me that MAGIC CONSTANTS work , but any WP CONSTANT will be unavailable .

That includes MY OWN constants that were declared in the plugin.php (actually this is the reason why I even began testing the WP constants )

Interesting enough - not only CONSTANTS are unavailable - but any wp function is returning "unavailable" .

PHP constant are meant to be available at all times through the app.. Is that a WP specific problem ? Is that intentional ? or am I doing something wrong ?

NOTE : I know there are other ways to do it (like using localize_script to pass variables to JS - or just use a function to output the path in the header) - but first - those methods will not be ideal for me - and more importantly is the fact that I want to understand why this method is failing ...

EDIT I :

Althouh @Matt Beckman pointed in the right direction his specific method did not work. It is true that a file from WP must be included . For me both the following work :

include("../../../../wp-load.php");
require_once (dirname(dirname(dirname(dirname(dirname ( __FILE__))))).'/wp-load.php');

Both as you can imagine are equal - but the problem remains : those are somewhat Hardcoded (like @Salman A) suggested - what if the plugin´s dir changes ?? what is the solution in that case ?

Note that the both wp-load.php and wp-config.php worked for me . I do not know what is better or which can present some security issues.

but I guess it is for another question ..

Bottom line : this solution is only TEMP until I will find the right answer . My plugin is loading via the WORDPRESS plugin mechanisem (enqueue_script() / register_script() / init() etc.. ) - and therefor I can not grasp why it does so.. Bu for now it works like described above.

Answer 1

Being that this is being included like JavaScript, your file.js.php needs to reference the Wordpress library in order to access those constants. Currently, as your code stands, it does not have any references to those constants.

__FILE__ does not need to access anything from Wordpress, which is why it works as expected.

You will need to include some require or include statements referencing the specific Wordpress PHP files you need at the top of file.js.php.

Edit

Use the following at the top of your file.js.php file to get access to those constants:

$home_dir = preg_replace('^wp-content/plugins/[a-z0-9\-/]+^', '', getcwd());
include($home_dir . 'wp-load.php');

Source