Include Facebook Javascript SDK In WordPress

I’m assuming you’re referring to the header.php file of your theme. In that case, it’s as easy as just enqueueing the script by appending this function to your theme’s functions.php file:

function enqueue_facebook_javascript_sdk(): void {
    wp_enqueue_script( 'facebook-javascript-sdk-initializer', get_template_directory_uri() . '/path/to/your/initializer.js' );
    wp_enqueue_script( 'facebook-javascript-sdk', 'https://connect.facebook.net/en_US/sdk.js', array(), null );
    return;
}
add_action( 'wp_enqueue_scripts', 'enqueue_facebook_javascript_sdk' );

The first JavaScript file should contain your version of the initializer from the docs, containing your appId.

In addition, the script requires the async and defer attributes. To add these, we insert a second function into functions.php:

function add_async_attribute( string $tag, string $handle ): string {

    if ( 'facebook-javascript-sdk' !== $handle ) {
        return $tag;
    }

    return str_replace( ' src', ' async defer src', $tag );
}
add_filter( 'script_loader_tag', 'add_async_attribute', 10, 2 );

Please let me know if this works for you.