How to use pre_render_block filter in WordPress

pre_render_block filter

The pre_render_block filter is a powerful filter allowing you to override the default rendering of a block and apply your customized block output. For instance, if you wish to alter the output of a core/paragraph block, this filter enables you to do so easily. It’s important to note that the modifications made using this filter are exclusive to the frontend display, ensuring a tailored user experience while leaving the edit page unaffected.

To use pre_render_block filter, first you have to register it using add_filter. You can write this code into functions.php of your activated theme or in a custom WordPress Plugin.

We at WePlugins, always prefer to create a custom WordPress Plugin while using hooks so nothing breaks when you update your WordPress Theme in the future.

In the below live example, we have defined a function modify_pre_render_block_defaults which takes 3 parameters and we registered using add_filter. The first parameter pre_render_block is the name of the hook, the second parameter modify_pre_render_block_defaults is the name of the function which needs to be called, the third parameter is the priority of calling the hook if the same hook is used multiple times, and the last parameter is the number of arguments (if any) to be passed in the registered function.

Sometime, you have to remove a registered hook so you can use remove_filter to remove pre_render_block filter.

Parameters

Below are the 3 parameters required to use this hook.

• $pre_render: (string|null) The pre-rendered content. Default null.
• $parsed_block: (array) The block being rendered.
• $parent_block: (WP_Block|null) If this is a nested block, a reference to the parent block.

Live Example

Below is an example of how you can use this hook.

    function weplugins_modify_pre_render_block_defaults($pre_render, $parsed_block, $parent_block) { 
        // Update the $pre_render variable according to your website requirements and return this variable. You can modify the $pre_render variable conditionally too if you want.
        return $pre_render; 
    }
    // add the filter
    add_filter("pre_render_block", "weplugins_modify_pre_render_block_defaults", 10, 3);
    

Custom Paragraph Styling Example:

This example shows how to add custom styling to paragraph blocks.

    function weplugins_custom_paragraph_styling($block_content, $block) {
        if ($block['blockName'] === 'core/paragraph') {
            // Add custom styling to paragraphs
            $block_content = '<div style="color: red;">' . $block_content . '</div>';
        }
        return $block_content;
    }
    add_filter('pre_render_block', 'weplugins_custom_paragraph_styling', 10, 2);
    

Dynamic Embed Replacement Example

This example demonstrates how to dynamically replace embed blocks based on custom logic.

    function weplugins_dynamic_embed_replacement($block_content, $block) {
        if ($block['blockName'] === 'core/embed') {
            // Replace default embed with a dynamic one based on custom logic
            $block_content = weplugins_get_dynamic_embed($block_content);
        }
        return $block_content;
    }
    add_filter('pre_render_block', 'weplugins_dynamic_embed_replacement', 10, 2);
    

Conditional Block Output Example

This example customizes the gallery block output only on single post pages.

    function weplugins_conditional_block_output($block_content, $block) {
        if ($block['blockName'] === 'core/gallery' && is_single()) {
            // Customize gallery output only on single post pages
            $block_content = '<div class="custom-gallery">' . $block_content . '</div>';
        }
        return $block_content;
    }
    add_filter('pre_render_block', 'weplugins_conditional_block_output', 10, 2);
    

To remove a hook callback, use the example below.

    remove_filter("pre_render_block", "weplugins_modify_pre_render_block_defaults", 10, 3);
    

Please make sure to provide the same callback function name, priority, and number of arguments while removing the hook callback.

Contact Us

If you need any customization or are having trouble using this hook, please contact us and we’d be happy to assist you.