php: how do i use a "global variable"?

2018-07-04 02:56:57

so my domain name is going to change from building it on my computer (localhost) to what my domain name will be when i actually deploy it, and I don't want to go back and have to change it in a million places. Now i know I could do a superglobal variable in php

<?php echo $GLOBALS['domain_name']; ?>

but as far as I know you can't use this in separate .js files. How can I create a "global variable" for my domain name that can be used in html and js?

Print in head of index file (or in php include in header tags)

Any js file can use variables defined in same scope level above it, even if in other files.

http://www.w3schools.com/js/js_scope.asp

Common form is to, inside the tag and at before any other calls, to define all 'global' js variables.

Printing php into a js file is discouraged highly for a few reasons, even though i have heard its possible, but just use a php include if you need it in multiple places:

<html>
<?php
  // include any shared content, in this case i include entire <head> section
  include('header.php');
?>
<body>

So if you have something like this at top of your php index file, or in an include you place there:

<script>
  var baseUrl = "<?php echo $GLOBALS['domain_name']; ?>";
</script>

Then that can be used as a standard variable anywhere after that point.

Side Note: using object wrapper

As a side note, you could wrap it in an object and pass that object through to other files, such as:

var AppData = {};
AppData.domain_name = "<?php echo $GLOBALS['domain_name']; ?>";
AppData.googleTrackerUID = "<?php echo $GLOBALS['gtrackerid']; ?>";
AppData.whatever = true;

fnct_from_earlier_point_or_elsewhere(AppData);

Thats only really of use if you think you may need to pass any other settings through, or just want to build for that possibility (especially if optional param, as easy to make reusable function that handles if an index doesnt exist)

I prefer the object approach, but dont overcomplicate if not needed.

EDIT

As @Amadan commented, it would even be easier to create the $AppData array/object in php then just call this:

var AppData = <?php echo json_encode($AppData); ?>;

Also, regarding someone posting to omit the 'var' keyword, its usually bad form as var doesnt stop it being global, and some issues with certain browsers (IE)

javascript var or not var, what's the difference?

You can inject any PHP value into clientside.

<script>
  var baseURL = <?php echo json_encode($baseURL); ?>;
</script>

Use json_encode because this gives foolproof safe way of delivering data in the format JS understands, and works on real arrays, PHP "arrays", numbers, strings, whatever you want.

try this:

<script>    
window.yourGlobalVariable = ....
</script>

by using you window it will be available for all your site

see: Define global variable in a JavaScript function

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