I am trying to get the current post ID in the render_callback function to generate related posts. However, the global $post object gives null.

I use this code for example from here:

add_action( 'init', function() {
    register_block_type('fc/related-posts', array(
        'render_callback' => function() {
            global $post;
            var_dump($post); // null

It will be fired on init but just $wp object works others like $wp_query or $post are null.

  • The actual render_callback won't be called until the template is being rendered though will it? Can you get a stack trace to work out exactly when it is being called?
    – Rup
    Jul 4, 2021 at 15:47
  • And it really shouldn't matter but I'd try var_dump( get_post() ); too, just to make sure there isn't some odd globals scoping problem with lambdas.
    – Rup
    Jul 4, 2021 at 15:57

2 Answers 2


When you declare your block, you need to tell WP that it needs context, either by using usesContext in JS/JSON or uses_context in PHP.

E.g in PHP:

        'render_callback' => 'render_my_block',
        'uses_context' => [ 'postId' ],

This value then takes an array of context identifiers, e.g. postId which can then be grabbed in the edit component for rendering, or in PHP at runtime:

function render_my_block( array $attributes, string $content, $block ) : string {
    $post_id = $block->context['postId'];

If you do not declare that your block requires the post ID then $block->context['postId'] will have no value.


I recently had the same issue. The workaround I used was to save the current post id as an attribute of the block:

const currentPostId = useSelect( ( select ) => {
    return select( 'core/editor' ).getCurrentPostId();
}, [] );

useEffect( () => {
    if ( currentPostId && currentPostId !== postId ) {
        setAttributes( { postId: currentPostId } );
}, [ currentPostId ] );
  • Thanks Phil, it will work but for me .getCurrentPostId() gives null as well. I could not understand what the problem is!
    – Amir 2mi
    Jul 8, 2021 at 12:10
  • Well that is weird. I believe getCurrentPostId() is an async function, so you need to make sure you are wrapping it with useSelect (or perviously a withSelect HOC) in your JS so that you are "subscribing" to any updates of the post ID.
    – Phil
    Jul 8, 2021 at 13:12
  • this won't work, especially if the block is inside a loop type block such as the query block, or in a template. There is no way to know the final post ID from the block editor, it has to be done in PHP when the block is rendered
    – Tom J Nowell
    Nov 21, 2022 at 15:01

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