Removes the block type on non-whitelisted post types

limitBlockToPostType.js

/**
 * Removes the block type on non-whitelisted post types
 *
 * @param  {Array}  postTypeNames An array of post type names as white list for this block
 * @param  {string} blockName     The name of the block
 *
 * @example
 * limitBlockToPostType( [ 'page' ], 'core/paragraph' );
 *
 * @return {void}
 */
export const limitBlockToPostType = function( postTypeNames, blockName ) {
	const comparePostType = ( selector, listener ) => {
		let previousPostTypeState = selector();
		return () => {
			const currentPostTypeState = selector();

			if ( currentPostTypeState && previousPostTypeState !== currentPostTypeState ) {
				previousPostTypeState = currentPostTypeState;
				listener( currentPostTypeState );
			}
		};
	};

	subscribe( comparePostType( select( 'core/editor' ).getCurrentPostType, ( postType ) => {
		if ( postTypeNames.indexOf( postType ) === -1 ) {
			wp.blocks.unregisterBlockType( blockName );
		}
	} ) );
};

We use this construct to handle a race condition. The block registry is being set up before the core/editor store so by the time we call registerBlockType we do not know yet on which post type we are. Thats why we subscribe to the store and once we get a non falsy response we check against an array of whitelisted post types. If the current post type is not in that array, we unregister the block.