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Let’s start with this, the param descriptions for wp_localize_script():

 * @param string $handle      Script handle the data will be attached to.
 * @param string $object_name Name for the JavaScript object. Passed directly, so it should be qualified JS variable.
 *                            Example: '/[a-zA-Z0-9_]+/'.
 * @param array $l10n         The data itself. The data can be either a single or multi-dimensional array.
 * @return bool True if the script was successfully localized, false otherwise.
 */
function wp_localize_script( $handle, $object_name, $l10n ) {

source

So you’re passing an array, right? Good.

If you’re not, tsk tsk. But let’s take a look at the good and the bad…

Array. Expected usage, you’re okay here:

wp_localize_script( 'jquery', 'exampleObject1', [
    'key' => 'value',
] );
// var exampleObject1 = {"key":"value"};

wp_localize_script( 'jquery', 'exampleObject2', [
    'value',
] );
// var exampleObject2 = ["value"];

String. Hit and miss:

wp_localize_script( 'jquery', 'exampleObject3', 'string' );
// var exampleObject3 = "string";

Above works by coincidence. This shouldn’t be relied upon.

wp_localize_script( 'jquery', 'exampleObject4', '' );
// var exampleObject4 = "";

Above throws a warning:

PHP Warning: Cannot assign an empty string to a string offset

Reduced example of the difference:

$l10n = 'string';
$l10n[0] = $l10n; // okay

$l10n = '';
$l10n[0] = $l10n; // warning. There's no character at the zeroth place to replace

Scalar. Miss (maybe hit because PHP is wacko):

wp_localize_script( 'jquery', 'exampleObject5', true );
// var exampleObject5 = true;

Above throws warning:

Cannot use a scalar value as an array

wp_localize_script( 'jquery', 'exampleObject6', false ); // no error
// var exampleObject6 = [""];

However, the above does not.

Reduced example, though it won’t really clarify things:

$true = true;
$false = false;

var_dump( is_scalar( $true ) ); // true
var_dump( is_scalar( $false ) ); // true

$true[] = 'adsf'; // Cannot use a scalar value as an array 
$false[] = 'jkl'; // okay why not

var_dump( $true ); // true
var_dump( $false ); // [ 0 => 'jkl' ] 

Why? No really, I’m asking.

---

So listen to the docs, and use an array.

A short post in the same vein as my last post, Don’t name form fields “update” or “link”.

We’ve probably all done something like this in one of our plugins:

$thing_title = apply_filters( 'the_title', $thing_title );

We want our thing’s title to get the same treatment as any other post title, so we use core’s filter. No big deal, right? Not so much.

In core, it’s actually used like this:

return apply_filters( 'the_title', $title, $id );

Importantly, it has an additional argument, $id, passed to it. source

Like with the accidental hook duplication in my last post, this means that callbacks expecting 2 arguments will end up throwing errors when the poorly-duplicated hook only provides one. Make sure when duplicating core hooks, all the expected arguments are passed.

In WordPress, every form field on the post edit screen results in a hook named pre_post_{$field} on save. Here’s how:

• All POSTed fields become part of the $post_data variable: https://xref.trepmal.com/wp/wp-admin/includes/post.php.source/#l191
• $post_data is passed to wp_update_post(): https://xref.trepmal.com/wp/wp-admin/includes/post.php.source/#l377
• wp_update_post() passes that on to wp_insert_post(): https://xref.trepmal.com/wp/wp-includes/post.php.source/#l3654
• wp_insert_post() passes that on to sanitize_post(): https://xref.trepmal.com/wp/wp-includes/post.php.source/#l3073
• sanitize_post() then calls sanitize_post_field() on each item: https://xref.trepmal.com/wp/wp-includes/post.php.source/#l1940
• sanitize_post_field() then creates a variable hook based on the key of each item: https://xref.trepmal.com/wp/wp-includes/post.php.source/#l2062

That means a field named “update” results in a variable filter hook named pre_post_update with 1 argument passed.

However, there’s a core action with that name already, and it passes 2 arguments: https://xref.trepmal.com/wp/wp-includes/post.php.source/#l3371

Similarly with link, there’s a core filter by that name already: https://xref.trepmal.com/wp/wp-includes/link-template.php.source/#l163

The problem?

If I have a form field named “update”, and I (or any plugin I’m running) hook into the core action like this:

add_action( 'pre_post_update', 'myplugin_pre_post_update', 10, 2 );
function myplugin_pre_post_update( $post_id, $data ) {
    // do stuff
}

Then the variable hook will call myplugin_pre_post_update but only pass the 1 argument. As of PHP 7.1, this will cause a fatal error

Besides, names as generic as ‘update’ and ‘link’ run the risk of conflict with another plugin.

Possible solution

If changing the field names isn’t feasible, you can adjust your callback:

add_action( 'pre_post_update', 'myplugin_pre_post_update', 10, 2 );
function myplugin_pre_post_update( $post_id, $data = null ) {
    if ( is_null( $data ) ) {
        // null $data means we're on the wrong hook instance, bail!
        return;
    }
    // do stuff
}

This is not a guide (yet?). These are just notes for personal reference which may be expanded upon later.

Site owners/developers/administrators may find useful hints below, but please do not get mad at me if you break your site.

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Methods were initially tested on a multisite-with-subdirectories installation, but are generally applicable to single and subdomain installations as well.

standard installation

familiar structure, e.g.

├── wp-config.php
└── wp-content/
    └── plugins/

nginx (subdirectory multisite)

if (!-e $request_filename) {
    rewrite ^(/[^/]+)?(/wp-.*)   $2                   last;
    rewrite ^(/[^/]+)?(/.*\.php) $2                   last;
}

Continue reading Notes: Renaming and relocating directories in WordPress