block: context

Used to create a context of data, for example between parent / children blocks.

Example, making the post id accessible, in block.json:

{
	"$schema": "https://schemas.wp.org/trunk/block.json",
    ...
    "usesContext": [ "postId" ]
}

In render.php :

$post_id = $block->context['postId'];

In edit.json :

export default function Edit( { attributes, setAttributes, context } ) {

// context.postId

}