In WordPress 4.7 the filter argument for any post endpoint was removed, The filter argument allows the posts to be
filtered using WP_Query public query vars. This plugin restores the filter parameter for sites that were
previously using it.
Use the filter parameter on any post endpoint such as /wp/v2/posts or /wp/v2/pages as an array of WP_Query
argument like so:
fetch( 'https://example.com/wp-json/wp/v2/posts?filter[name]=the-slug');