Update the block through ajax

Question

I have added a block which shows the no of items added to an entity. I want to refresh the block through ajax as the items are added to an entity through ajax form so whenever I add an item, it will refresh or re-render the block content too.

I found some of the modules, but they are in Drupal 7 and not available for D8 so I want to make it done with my custom module but didn't find anything useful.

UPDATED

I have added the class attribute with the block and whenever I add any items, I made an ajax request through javascript which calls the respective controller and at the same time, I run this too--

// This is a part of the controller function from where I am calling below defined methods.
$this->updateBlock();

protected function getBlock() {
    $block = $this->blockManager->createInstance('block_id', []);
    return $block;
}

public function updateBlock() {
    $block = $this->getBlock();
    $this->response->addCommand(new ReplaceCommand('.block--class', $block->build()));
    return $this->response;

}

But It is not updating the block.

Answer 1

Important part you left out is what kind of ajax, is it a form you are submitting or custom javascript which uses ajax to target a controller endpoint? As this is how we return the code of the block.

But the code you are looking for re-rendering a block is:

$id = '' // the number of the block_id
$block = \Drupal\block_content\Entity\BlockContent::load($id);
$render = \Drupal::entityTypeManager()->getViewBuilder('block_content')->view($block);
return $render;